There is a huge gap between knowledge and practice, and between what is known through research and what is actually implemented in public mental health systems. In the past 2 decades, rigorous research has demonstrated the effectiveness of various treatments and interventions but these findings have not resulted in broad-based implementation. A major contention of this article is that while there is a growing body of knowledge related to evidence-based practices, there is a lack of understanding and research related to factors critical for implementation. This article reviews the current status of implementation of evidence-based practices in the public mental health system and identifies challenges and barriers related to their dissemination. Based on this analysis, this article proposes a research agenda that promotes the development of a science of implementation of evidence-based practices.