This article examines the legal status of "soft law" in the fields of medicine and medical research. Many areas of clinical practice and research involve complex and rapidly changing issues for which the law provides no guidance. Instead, guidance for physicians and researchers comes from what has often been called "soft law"--non-legislative, non-regulatory sources, such as ethics policy statements, codes, and guidelines from professional or quasi-governmental bodies. This article traces the evolution of these "soft law" instruments: how they are created, how they are adopted within the professional community, and how they become accepted by the courts. It studies the relationship between soft law instruments and the courts. It includes an examination of the approaches to judicial analysis used by the courts in theory and in practice. The authors then examine the jurisprudence to see how courts will adopt professional norms as the legal standard of care in some circumstances and not others. They consider the legal concerns and ethical issues surrounding the weight attached to professional practices and norms in law. The authors demonstrate how practices and policies that guide professional conduct may ultimately bear weight as norms recognizable and enforceable within the legal sphere.