The best evidence should inform all clinical decisions, but physicians cannot realistically keep up with all of the literature. Two types of preprocessed evidence that can help busy clinicians incorporate evidence into everyday medical decision-making are systematic reviews and clinical practice guidelines. However, conclusions of systematic reviews and recommendations of evidence-based clinical practice guidelines should not be accepted at face value. Like primary studies, they must adhere to rigorous standards in order to reduce error and bias. In fact, low-quality systematic reviews and guidelines can be very misleading. This article discusses what factors distinguish a high-quality systematic review. It also examines the difference between systematic reviews and clinical practice guidelines, and what factors distinguish a high-quality guideline. A separate article discusses how to interpret and apply systematic reviews and clinical practice guidelines, particularly when evidence is weak or inconclusive, or when different systematic reviews or guidelines are discordant.