Introduction: No educational method or combination of methods will facilitate implementation of clinical practice guidelines in all clinical contexts. To develop an empirical basis for aligning methods to contexts, we need to move beyond "Does it work?" to also ask "What works for whom and under what conditions?" This study employed Success Case Method to understand how 3 performance improvement CME activities contributed to implementation of tobacco cessation practice guidelines in 9 outpatient practices. Methods: Success criteria were applied to clinical data from 93 practices, generating a pool of 14 success cases; 9 were recruited into the study. We conducted semistructured telephone interviews with 1 to 4 informants in each practice. Individual case reports were developed summarizing changes made, what was done to effect the changes, relevant contextual factors, and contributions of the educational interventions to change. A cross-case analysis followed. Results: Twenty informants were interviewed. Practice changes varied in number and degree. Implementation mechanisms included acquisition of new knowledge and skills, making improving cessation practice an active goal, engaging the clinical team, adopting a more proactive approach with smokers, and making smokers and clinical practice performance more visible. Contextual factors influencing the implementation process were also identified. Discussion: The study shows that (1) the appropriate target of an educational intervention may be a team rather than an individual, (2) implementing even relatively simple practice guidelines can be a complex process, and (3) change requires scientific and practical knowledge. A richer understanding of implementation mechanisms and contextual factors is needed to guide educational planning. (Contains 2 tables, 2 figures and 1 footnote.)