A large number of organizations are currently developing practice guidelines in oncology. These include federal agencies; medical societies and groups, including both oncologic and nononcologic specialty societies; and informal and formal groups of oncologists at the national, regional, and local level. Despite this marked increase in guideline activity, the science of guideline development must still be considered embryonic. Several general principles appear to be important for the generation of sound practice guidelines: (1) selection of suitable topics; (2) appropriate composition of the panel; (3) objectivity of the process used to arrive at recommendations; and (4) specific provisions for review and revision. Like the science of guideline development, the science of guideline implementation is still in its infancy. The factors facilitating physician acceptance of guideline recommendations have yet to be identified. Also, systematic evaluation of the effectiveness of different implementation strategies is needed.