Bad breath typically originates in the mouth, often from the back of the tongue. Nasal problems also can cause bad breath; odor generated in this manner can be easily distinguished from mouth odor by comparing the odor exiting the mouth and nose. In most cases, good professional oral care combined with a daily regimen of oral hygiene--including interdental cleaning, deep tongue cleaning and optional use of an efficacious mouthrinse---will lead to improvement. This article discusses common causes of oral malodor as well as methods to assess the extent of the problem.