Concepts and methods in professional practices evaluation are often confused. After a description of the classical conceptual framework, we present these methods in an approach in which practice is the principal result to be measured. Thus it makes it possible to apply the traditional epidemiological concepts to the evaluation of the professional practices with their three traditional fields: 1) In the descriptive approach, cross-sectional practice studies allow an observation and description of the usual behaviors, possibly compared to references. The methodological constraints are the same as which of descriptive epidemiological studies; 2) In the analytical approach, factors associated with practice - simple or conformed to criteria - are evidenced on a representative sample; 3) In the evaluative approach of practices improvement, the objectives are the assessment of formative, organizational or structural interventions, aiming at modifying practices. Three types of studies are to be used: quasi experimental in which clinical audit is the reference method in the field of medical care. The six main steps of clinical audit are described; experimental, based on the community randomized trial scheme, which have the advantage to provide results that can be immediately generalized; observational in which no control on the implementation of intervention is done. "Here and else" and "before and after" studies are used. To be effective for evaluation of professional practice, theses methods must come within the scope of a favorable institutional context.