This is part of the series of practice guidelines commissioned by the Infectious Diseases Society of America through its Practice Guidelines Committee. The purpose of this guideline is to provide assistance to clinicians in the diagnosis and treatment of community-acquired pneumonia. The targeted providers are internists and family practitioners. The targeted groups are immunocompetent adult patients. Criteria are specified for determining whether the inpatient or outpatient setting is appropriate for treatment. Differences from other guidelines written on this topic include use of laboratory criteria for diagnosis and approach to antimicrobial therapy. Panel members and consultants are experts in adult infectious diseases. The guidelines are evidence based where possible. A standard ranking system is used for the strength of the recommendations and the quality of the evidence cited in the literature reviewed. The document has been subjected to external review by peer reviewers as well as by the Practice Guidelines Committee and was approved by the IDSA Council. An executive summary and tables highlight the major recommendations. The guidelines will be listed on the IDSA home page at http://www.idsociety.org.