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. E v i d e nc e -b a se d m e di c i n e (EBM) is commonly defined as "the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients."1 The term is loosely used and can refer to anything from conducting a statistical meta-analysis of accumulated research, to promoting randomized clinical trials, to supporting uniform reporting styles for research, to a personal orientation toward critical self-evaluation. EBM was initially defined in opposition to clinical experience, but later definitions have emphasized its complementary character and have aimed to improve clinical experience with better evidence.2 One common implementation of EBM involves the use of clinical practice guidelines during medical decision making to encourage effective care. The Institute of Medicine (IOM) defines clinical guidelines as "systematically developed statements to assist practitioner and patient decisions about appropriate health care for specific clinical circumstances."3 An expert committee does the work of sifting through the scientific literature for clinicians and offers coherently sequenced recommendations based on the best available evidence aimed at everyday decision-making situations. Guidelines can be applied to any aspect of clinical care: how and when to order diagnostic or screening tests, when to provide certain medical services, how these should be performed, and how long 1 8 J a n u a r y / F e b r u a r y 2 0 0 5 H i s t o r y & C o n t e x t