PMC policies and processes are guided by those of the National Library of Medicine (NLM) and National Institutes of Health (NIH), as well as current best practices for scientific publishing and scholarly communication. The NLM Board of Regents provides oversight of PMC; from 1999 through 2017, the PMC National Advisory Committee also advised on the content and operation of the repository.
Though journal and publisher representatives are the primary audience for this page, anyone interested in NLM’s quality standards and expectations for PMC journals is encouraged to start here.
In June 2003, the PMC National Advisory Committee affirmed the policy that journals joining PMC must make the full text of their deposited content viewable in PMC, and endorsed the following participation guidelines:
- Journals are encouraged to deposit the complete contents of each issue, not just research papers or other selected parts, in the PMC archive.
- Journals are encouraged to provide this content to PMC as close to publication as possible, regardless of when they allow it to be publicly accessible, as this makes it easier for them to correct errors detected in the journal's files during PMC's data review process.
- Journals are encouraged to allow their primary research articles to be viewable in PMC as early as possible but generally less than one year from publication date.
- Journals are encouraged to allow all other journal content (e.g. letters, reviews, etc.) to be viewable in PMC as early as possible but generally less than three years from publication date.
These original guidelines are the foundation for the current PMC participation agreement, made between the journal owner (or journal owner’s legal representative) and NLM, which includes additional provisions for the timing of deposit and availability of content.
There are three options available for participating in PMC. Each option requires the journal owner or journal owner’s legal representative to sign a PMC Participation Agreement. The eligibility requirements for each option are described below.
Full Participation Agreement
Full Participation participants commit to depositing the complete contents of each issue or volume of a journal, starting with a particular volume/issue or publication date in accordance with PMC’s Back Content policy.
To be eligible for inclusion under this type of agreement a journal must satisfy NLM’s Scientific Quality and Technical Quality standards for PMC journals.
NIH Portfolio Agreement
NIH Portfolio participants commit to depositing the final published version of all NIH-funded articles (as defined by the NIH Public Access Policy) from a journal, starting with a particular volume/issue or publication date. The participant may choose to also deposit additional, non-NIH-funded articles under this agreement. NIH-funded authors will be blocked from depositing manuscripts themselves from the journal via the NIH Manuscript Submission System from the starting date of deposit indicated in the agreement.
As of May 1, 2018, to be eligible for inclusion under this type of agreement a journal must be currently indexed in MEDLINE and regularly publish articles supported by NIH (or other PMC partner or Europe PMC funders.)
Selective Deposit Agreement
Selective Deposit participants deposit a more loosely defined set of content to PMC than what full participation and NIH portfolio participants agree to. Selective Deposit is intended for the deposit of a subset of articles from a collection of journals. This model is frequently used by publishers who offer a hybrid publishing model, i.e., subscription-based journals in which selected articles are published as Open Access, or publishers who wish to support the policies of a particular funder which require articles to be made available in PMC under specific license terms.
To be eligible for a Selective Deposit agreement, a publisher must
- have an established peer review process for all of its journals.
- have an open access publishing program and/or a program for helping authors comply with the public or open access policies of funders that use PMC or Europe PMC as a repository (i.e., partner funders).
- publish journals that are indexed in MEDLINE and/or a high volume of articles supported by partner funders.
- demonstrate compliance with industry standards/best practices.
As of May 1, 2018, individual articles are eligible to be deposited in PMC as part of a Selective Deposit collection if the journal of publication is currently indexed in MEDLINE or the work is funded by NIH or other funders that require deposit in compliance with their public or open access policies (see PMC and Research Funder Policies for details).
Expectations for PMC Participants
For a journal to participate in PMC, NLM expects that the journal and publisher will meet NLM’s standards for PMC and the NLM Collection over time. These standards include maintaining the scientific quality of the publication, supplying quality data to the archive, following industry best practices, demonstrating sustainability, and adhering to NLM Collection requirements. More details on each of these expectations is provided in the following sections.
NLM considers the suitability of a journal for the NLM Collection and its scientific and editorial quality in determining if it merits inclusion or continued archiving in PMC. See Journal Selection for PMC for details.
Journals that have been reviewed by the Literature Selection and Technical Review Committee (LSTRC) and are fully indexed for MEDLINE generally will not require further scientific review for PMC.
See Reevaluation for information on when NLM may reevaluate a PMC journal and the reevaluation process.
A journal must provide PMC with the full text of articles in an XML (eXtensible Markup Language) format that conforms to an acceptable journal article DTD (Document Type Definition) and meets the Minimum Data Criteria. NLM recommends that data be submitted in XML conforming to the NISO JATS Journal Publishing Tag Set, but PMC will also accept data in other full-text article DTDs that are widely used in life sciences journal publishing.
PMC does not accept articles in HTML format.
Files required for each deposited article:
- A separate XML data file for the full text of each article.
- The original high-resolution digital image files for all figures in each article.
- A PDF, if one exists, in addition to the XML version (but not as the only form).
- Supplementary material files (e.g., spreadsheets or video files) available with the article. (See Supplementary Material policy)
PMC-participating journals must continue to meet PMC’s Production Data Requirements consistently in order to remain in PMC. If a journal does not continue to meet these standards, NLM may terminate a journal’s participation agreement.
NLM looks for ongoing publisher conformance with guidelines and best practices published by professional organizations, including Recommendations for the Conduct, Reporting, Editing, and Publication of Scholarly Work in Medical Journals (PDF) from ICMJE and Principles of Transparency and Best Practice in Scholarly Publishing (joint statement by COPE, DOAJ, WAME, and OASPA).
If a publisher is found to not be following established industry best practices, NLM will cease collecting the publisher’s journals and not accept applications to any of the NLM Literature databases, including PMC and MEDLINE, for a minimum of three years.
NLM expects a participating journal to have a posted publishing schedule, maintain its stated publishing schedule, and actively publish primary content.
If a participating journal repeatedly fails to publish primary content, does not adhere to its stated publishing schedule, or does not publish any primary content over a two-year period, PMC will terminate the journal's participation agreement. The journal may reapply if/when it resumes publishing, subject to the minimum requirements for reapplications.
Access to Electronic Resources
To be considered for PMC, a journal that is accessed or delivered electronically (i.e., e-journal) must provide at least one of the following means of institutional access as defined in the NLM Collection Development Guidelines (CDG):
- access to full text with no requirement for user registration; or
- licensed institutional access, including IP authentication and compliance with interlibrary loan provisions and other NLM requirements.
E-journals that are selected for inclusion in PMC must remain compliant with the NLM CDG requirements. If a journal is found to no longer meet the access requirement, PMC will work with a journal or publisher to ensure a timely resolution to the problem. A temporary hold will be placed on adding new content to PMC until the situation is resolved. If the access issue is not resolved within six months, the journal’s participation agreement will be terminated.
E-journals are also encouraged to follow the recommendations of PIE-J: The Presentation & Identification of E-Journals (NISO RP-16-2013), particularly in the areas of title presentation, accurate use of ISSN, and citation practices.
The application and selection processes for PMC are described in detail at How to Include a Journal in PMC and Journal Selection for PMC. If a journal is not selected, a reapplication timeframe will be provided to the applicant at the time of rejection. Applicants are expected to be responsive to NLM queries and requests throughout the entire application process.
Upon selection, NLM continues to monitor journals for conformance with NLM’s expectations for PMC Participants to maintain the quality of the archive.
NLM selection decisions for PMC applications are generally final and not subject to appeal except in the limited circumstances described in the NLM Appeals policy for MEDLINE and PMC.
First-Time Applicants & New Participants
If a publisher has not previously submitted a journal application to NLM (for MEDLINE or PMC), NLM will generally complete a review of the publisher policies and practices upon receipt of an application (See Publisher Practices). This review determines whether a publisher’s journals are eligible to be considered for the NLM Collection. A publisher review is completed prior to initiating the journal application process. As such, the application period will be longer for these titles. NLM may also request additional publisher information as part of this review.
New participants must complete the PMC application process (including technical evaluation) with one journal and that journal must meet PMC’s Production Data Requirements for at least six months before the publisher can submit an application for a second title.
A publisher may have up to two journal applications at a time in the PMC Evaluation and Setup Process if they already have at least one PMC-participating journal that meets all of the following criteria:
- The journal successfully passed the Scientific Quality Review;
- The journal successfully passed the Technical Evaluation and Pre-Production phase;
- The journal has been released to the live site and has continuously met the Production Data Requirements for the past six months.
For publishers that have not previously applied to PMC with a journal that meets the criteria above, the publisher is eligible to have one journal at a time in the Evaluation and Setup Process.
PMC may consider more than two applications at a time from publishers with ten or more PMC-participating journals that have successfully passed the Evaluation and Setup Process and met the Production Data Requirements for the past six months.
Reapplication timelines will vary based on several factors:
- Journals that do not pass the initial application screening or meet PMC's Scientific Quality Standard are eligible to reapply two years (24 months) after the date the review is completed.
- Journals that do not pass PMC's Technical Evaluation are eligible to restart the process one year (12 months) after the date the technical evaluation is completed.
- Journals that cease participation as a result of not meeting PMC's Publishing Schedule or Access to Electronic Resources policies are eligible to reapply when they resume publishing in line with the applicable policy and meet the pre-application requirements.
Any reapplication to PMC will be processed as a new application and will be subject to initial quality screening, scientific quality review, and technical evaluation (when applicable).
If a journal reapplies after previously not meeting PMC's Scientific Quality Standard, a minimum of 20 peer-reviewed articles (e.g., original research or review articles, clinical case reports) must have been published between the initial notification from PMC and the date the journal is eligible to submit a new application. If a journal has not published a minimum of 20 peer-reviewed articles by the date it is eligible to reapply, the journal should wait until the minimum has been met before submitting the new application. Please note that any content published prior to the date of the previous rejection is ineligible for inclusion in the PMC archive and is, therefore, out of scope for a PMC journal review.
An application will be considered expired and closed after two years if the journal has not completed all the steps in the evaluation and setup process or ceases to respond to PMC communications.
To maintain the quality of the archive, NLM regularly reviews current PMC journals for conformance with NLM's Expectations for PMC Participants.
NLM will reevaluate a journal for continued participation in PMC if
- there are problems identified with article(s) that a publisher fails to address or that appear to be systemic;
- there are verifiable concerns about the scientific or editorial quality of the journal content; or
- there are significant changes in a journal's ownership, policies, subject matter scope, editorial board, or practices.
The reevaluation process for a PMC-participating journal is similar to the review process for new journal applications to PMC, including evaluation by external consultants. See Journal Selection for PMC for details on how journals are assessed. If a journal was accepted for archiving in PMC by virtue of its inclusion in MEDLINE, the reevaluation process will involve the Literature Selection Technical Review Committee.
Before the reevaluation begins, PMC staff will notify the journal of NLM’s concerns and place a hold on processing any additional content until the review is complete. The reevaluation process will focus on recent content and may take up to 12 weeks.
To begin the process, the publisher must submit an application to the PMC Publisher Portal. If an application is not received within 90 days of being notified by NLM, the journal's participation agreement will be terminated.
If the journal is found to meet NLM's scientific and editorial standards for PMC, PMC will continue to accept content from the journal, including all articles published during the holding period. If the journal is found to no longer meet NLM’s standards, the PMC agreement will be terminated, and the journal will be eligible to reapply two years after the date of the termination. No additional content, including any articles submitted or published during the holding period, will be accepted for archiving in PMC. An exception will be made on a case-by-case basis for critical updates (e.g., corrections or retractions) to articles already archived in PMC.
NLM's decision to deselect a journal from PMC is final. NLM encourages journals to use feedback resulting from the reevaluation review to improve the publication's overall scientific and editorial quality.
NLM may reevaluate a journal after a title change if it is accompanied by significant changes in editorial policies, editorial board, or subject matter scope. In such a case, a hold will be placed on adding new content to PMC and the journal will be asked to submit an application once 20 articles have been published or after one year (as long as there is sufficient primary content available for review). See the Reevaluation section above for further details of the process.
Journal Eligibility Guidelines
A journal is eligible to submit an application to PMC as long as it meets the following criteria regarding scope and language as well as the pre-application requirements outlined on the How to Include a Journal page.
Journal Scope and Content
Before evaluating the scientific and editorial quality of a journal, NLM will consider the subject matter, presence of publicly stated policies, article content types, and other scope-related matters. A journal should be in scope for the NLM Collection, broadly, as well as PMC, specifically, to be considered for inclusion in the archive.
Journals that do not clearly meet the subject scope and content requirements for the NLM Collection and PMC may require more in-depth review. In such cases, the application period may need to be extended or the applicant may be encouraged to reapply at a later date if the journal scope evolves.
NLM Collection Scope
To be eligible for PMC, a journal must publish generally within the biomedical and life sciences. The NLM Collection Development Guidelines defines NLM’s collecting interest in a subject, and the level of intensity at which it is applied. NLM focuses on the subject matter of the peer-reviewed content that a title has published in the last two years, especially as it pertains to human health and medicine as per the NLM legislative mandate, to determine whether a journal is in scope for the Collection. NLM is unable to provide a comprehensive list of articles reviewed in making a scope determination.
In addition to the criteria for journals described in the NLM Collection Development Guidelines, NLM considers the following factors in determining if a journal is in scope for PMC:
- The journal must be peer reviewed and have a clearly stated peer review policy.
- The primary content should consist of one or more of the following article types:
- Original research
- Review articles
- Clinical case reports
- Data descriptor articles (Note: Articles must point to dataset that is publicly accessible.)
- Descriptions of clinical or surgical procedures
- Analyses of philosophical, ethical, or social aspects of the health professions or biomedical sciences
- The affiliations of the editors and authors should reflect the journal’s scope and demonstrate editorial independence and diversity.
- The journal must be responsible for the peer review process and editorial processes underlying the published articles.
To support the MEDLINE Policy on Indexing Electronic Journals, PMC will accept applications from non-English MEDLINE journals.
For non-MEDLINE journals, NLM requires the primary content to be largely in English before an application can be submitted, as NLM only has the resources to review English-language content for PMC at this time. The scientific and editorial quality of the English-language content will be assessed following PMC’s standard selection process. Multilingual journals that publish additional non-English content are encouraged to publish English-language abstracts and titles for these articles.
If a journal with non-English content is accepted for archiving, the complete contents of each volume/issue, regardless of language or MEDLINE status, should be deposited in PMC to ensure full coverage in the archive.
This section outlines PMC expectations for the handling and deposit of different types of content. Additional guidance can be found in the PMC Tagging Guidelines.
Online First (OLF) Articles
Online First (OLF) articles are article versions published online on a continuous basis, as soon as they are ready for publication (after peer review and editing, etc.) instead of, or in addition to, being published in a collection of articles as an “issue” on a periodic basis. Other common labels for this version of an article include “ahead of print” and “early edition.” PMC generally does not accept OLF articles when they are not the final, published version of the article (version of record). An exception may be made for an article that needs to be available in PMC immediately in order to satisfy a funding agency’s policy.
PMC will accept OLF articles from a journal that considers the OLF version to be the version of record if the journal
- is currently indexed in MEDLINE,
- meets PMC’s Production Data Requirements, and
- successfully completes a pilot phase for OLF submission.
Journals that deposit the OLF version must deposit the OLF and corresponding issue version of every article in all cases.
Participants should indicate the earliest volume/issue of the journal to be provided to PMC for archiving at the time the agreement is signed. Full-participation PMC journals that are also indexed by MEDLINE may deposit back content as far back as the earliest volume/issue indexed by MEDLINE. Generally, non-MEDLINE journals may deposit content that was published up to two years prior to the date of PMC acceptance, unless
- the journal was determined by NLM to be out of scope for PMC during that period;
- the journal was determined by NLM to not meet PMC quality standards during that period; or
- the journal did not consistently meet the language guidelines for PMC during that period.
All content deposited must meet the Minimum Data Criteria.
For any revision to or error in an already-published article, PMC requires the submission of a published notice of correction, which should include its own complete citation information. This notice should specify the exact nature of the error, along with the citation information for the corrected article, as seen in the following:
The guidelines for submitting the correction notice are the same as for other PMC articles and should comprise an XML and PDF file, as well as any relevant image and supplemental files. The XML source file must also include structured citation information about the corrected article in order to link it to the correction notice. For specific details, please see the PMC Tagging Guidelines.
Corrections are made available immediately in PMC without embargo.
Journals that decide to republish a corrected version of the article should also see Corrected and Republished.
Corrected and Republished Articles
A journal may correct a previously published article by republishing the article in its entirety, either
- to rectify an editorial or printing error; or
- to correct scientific errors.
Generally, these cases are handled with the publication of a correction notice, specifying the exact nature of the error (see also Corrections). In some cases, though, as per the ICMJE, "Errors serious enough to invalidate a paper's results and conclusions may require retraction" (see also Retractions). If the journal decides to correct the errors and republish the article following a retraction, NLM expects the archived republication to have updated citation metadata, including a unique DOI and revised publication date to facilitate citation and discovery of the updated work and retain the transparency of the scholarly record. The republished version should include details of the changes from the original version. Guidance on tagging republications is available in the PMC Tagging Guidelines.
When an article is corrected and republished, PMC will indicate from the original article that there is an update available and link to the republished version but will not remove the original article from the archive.
In the event that a publisher discovers a serious problem with an article that exceeds the need for a traditional correction or erratum notice, such as in cases of scientific misconduct, plagiarism, pervasive error or unsubstantiated data, then the journal must publish a notice of retraction. Retraction notices should follow NLM's MEDLINE policy on retractions and clearly state that the article is being retracted, and should be published in citable form. The notice should also clearly specify the reason that the article is invalid. Please note that this policy is consistent with the standard practice of most scientific and scholarly journals and established industry best practices (e.g., ICMJE's Recommendations for the Conduct, Reporting, Editing, and Publication of Scholarly Work in Medical Journals, and COPE's Guidelines for retracting articles).
In PMC, a retracted article is marked boldly and includes a link to the retraction notice, as in this example. To create this link, the XML source for the retraction must be tagged with structured citation information about the retracted article in order to link it to the retraction notice. For specific details please see the PMC Tagging Guidelines.
PMC will not remove retracted articles from its archive. However, on occasion NLM will suppress an article from public view upon consultation with the publisher if the case involves a legal injunction or a breach of patient privacy. In order to fulfill its role as a permanent archive and maintain the historical record, NLM will retain the subject item in the internal PMC archive, but prevent access to it via the public PMC website. PMC users will be able to see a citation for the article and a notice indicating that, for legal reasons, the publisher has withdrawn permission to display the item in PMC. Retractions are made available immediately in PMC without embargo.
Journals that decide to republish a corrected version of the article should also see Corrected and Republished.
Other Types of Content
For an NIH Portfolio journal or a Full Participation journal with an embargo of 12 months or less, PMC will submit a citation to PubMed as soon as the article is fully processed through our system. Please note that, for any non-MEDLINE journal, only PMC can submit the journal's citations to PubMed. An exception may be made if a journal has no embargo. Citations usually appear in PubMed within 24 hours of submission.
MEDLINE-indexed journals may submit their own citations.
PMC expects publishers to follow the International Committee of Medical Journal Editors (ICMJE) recommendations on “Supplements, Theme Issues, and Special Series” and the NLM guidance Conflict of Interest Disclosure and Journal Supplements in MEDLINE.
The policy applies to journal supplements in PMC that involve any commercial sponsorship of the published research or the publication itself. In such cases, every article must include a statement clearly indicating any conflict of interest or potential influence that the commercial institution may have had on the reported findings and conclusions contained therein.
Examples of sponsored supplements to which the PMC policy applies:
- A special issue sponsored in its entirety by an outside for-profit organization
- A special section or group of articles whose authors have financial ties to a sponsoring for-profit organization
- Reports from a conference sponsored by an outside for-profit organization
- An issue or group of articles devoted to a special topic related to a proprietary product.
PMC mandates that the disclosure of conflicts of interest on the part of authors and editors must appear on each article. This statement must include the role of the sponsoring organization and any financial relationships with respect to the sponsoring group or its commercial products. The disclosure statements must appear within the article, as opposed to a blanket disclosure appearing elsewhere in the issue.
Specifically, for supplements submitted to PMC:
- Where ALL articles are authored by employees of a commercial sponsor, the content will not be posted in the archive
- Where the supplement has ANY commercial sponsorship, the role of the sponsor and the relationships of the authors to the sponsor are required on each article. Where no relationship exists, that should be explicitly stated on each article as well.
- For supplements with NO outside support, each article should specifically state that the authors have nothing to disclose.
See the Funding Information section in the PMC Tagging Guidelines for technical guidance on tagging funding information and conflict of interest statements.
Any supplementary material files (datasets, images, tables, video, or other documents / files) that are associated with an article must be deposited in PMC with the article. This applies to all files made available in the article record, even if the files are also available in a public repository. An exception may be made for files that require custom software to read/use or that are very large (over 2GB). For specific submission requirements for PMC data providers see the File Submission Specifications.
NLM encourages publishers to supply unique identifiers for supplementary material. In cases where the publisher has not assigned a unique ID to a supplemental file, NLM will generate and display in the Associated Data Box a Globally Unique Identifier (GUID) to support the reporting of supplemental datasets as well as the citation and discovery of this content.
In cases where supplementary materials cannot be reasonably included with an article, either in a figure, table or supplementary file, NLM encourages journals and authors to make the content available in a public repository and include the relevant data citation(s) in the paper. Guidance for PMC data providers on tagging data citations is available in the PMC Tagging Guidelines.
The NIH Manuscript Submission (NIHMS) system can accept submissions of datasets (2 GB or smaller) in support of any manuscript files deposited in compliance with a partner funder’s public or open access policy. Because these datasets will be publicly accessible, those related to human subjects research should not include any personally identifiable information and deposits should be consistent with informed consent. For more information on depositing supplementary data and dataset files via NIHMS, see the related NIHMS FAQ.
Access and Display
Once archived in PMC, the availability, display, and use of articles may be limited by embargoes, copyright restrictions, or other policy considerations. This section provides an overview of when articles may be released for public view and what links may be displayed from the article.
Information about copyright restrictions and restrictions on the systematic downloading of articles is available in the PMC Copyright Notice.
Participating journals can choose a default embargo to delay the release of articles on the PMC website. This embargo is calculated from the article publication date and is defined in the journal’s PMC Participation Agreement. The maximum embargo allowed is typically 12 months after publication. A request for a longer embargo requires approval from NLM.
The default embargo is set automatically by PMC at the journal level, however, the participant can choose to override the default embargo for individual articles using a processing instruction (PI) in the XML. See the PMC Tagging Guidelines Processing Instructions section.
Please note that regardless of any journal-level embargo, NLM does not embargo Open Access (OA) articles, corrections, retractions, or editorial expressions of concern.
PMC will consider adding external links in reference lists to aid users in discovering and accessing content cited in PMC articles if all the following criteria are met:
- Links must be of potential use to NCBI/NLM database users. Useful links will expand upon information already found in PMC.
- Link provider has been widely adopted by major scientific publishers and platforms.
- Link provider prioritizes discovery of the publisher’s full-text as the version of record.
- Link provider responds to complaints regarding copyright infringement and complies with the PMC Copyright Notice.
- Links should deliver the relevant information to users with few or no intermediary steps.
- Inclusion of links should not unnecessarily overburden NCBI resources.
PMC can only include external links in reference citations that are to the reference source, not to related content.
The label of the link in the PMC display will be that of the link provider.
PMC is a service of the National Library of Medicine, a Federal agency, and as such it is produced using Federal computer and network facilities. Because these types of public facilities cannot be used for private commercial advertisement, endorsement, or competition, special care must be taken by resource providers with a commercial interest in linking from PMC.
Resource providers should not attempt to use PMC as a form of advertising. Resource providers found willfully disregarding these guidelines will be barred from further inclusion in PMC.
See also the PMC Disclaimer for information on Endorsement and External Links.