Publisher Summary This chapter presents a comprehensive overview of evidence-based medicine (EBM). The top five levels of evidence that are usually considered in EBM consist of study designs that provide systematic clinical observation and that are borrowed from the scientific methods of epidemiology. It is found that randomized trials rank higher on the hierarchy of evidence and systematic reviews of randomized trials rank higher still. While EBM was originally intended to be an approach to clinical decision making carried out by individual physicians, the movement has been forced to adapt to deal with a variety of practical constraints. The initial formulation of EBM seemed to require an almost algorithmic approach to decision making according to which an individual physician assesses the evidence and then applies it to the particular case. The later versions of EBM arguably deal with the need for individualized care, as well as the importance of incorporating patient values, by suggesting that medical research should be conscientiously and judiciously applied to patients.