This is an update of the 1997 Quality Standards for Immunization, which is one of a series of guidelines commissioned by the Infectious Diseases Society of America (IDSA) through its Practice Guidelines Committee. This information is presented as a standard-of-care rather than practice guidelines because the evidence for following these recommendations is so strong that they should be implemented with rare exceptions. The purpose of these standard-of-care guidelines is to provide assistance to clinicians who make decisions on providing immunizations to infants, children, adolescents, and adults. This document is a summary of evidence-based guidelines previously developed by national organizations. A standard ranking system was used to determine the strength of the recommendations, and the quality of evidence cited in the literature was reviewed for each guideline. The targeted health care professionals are pediatricians, family practitioners, internists (including specialists), obstetricians, and others who provide immunizations. The panel members are experts in the field of adult and pediatric infectious diseases. The document has been subjected to external review by peer reviewers as well as by the Practice Guidelines Committee, and it was approved by the IDSA Council. Indicators for measuring compliance with the standards are included. The document will be posted on the IDSA home page at http://www.idsociety.org/.