Evidence-based medicine (EBM) aims to address the persistent problem of clinical practice variation with the help of various tools, including standardized practice guidelines. While advocates welcome the stronger scientific foundation of such guidelines, critics fear that they will lead to "cookbook medicine." Studies show, however, that few guidelines lead to consistent changes in provider behavior. The hopes, fears, and mixed record of EBM are rooted in the traditional professional perspective of the clinician as sole decisionmaker. Multifaceted implementation strategies that take the collaborative nature of medical work into consideration promise more effective changes in clinical practice.