The World Medical Association's (WMA) Declaration of Helsinki is one of the most important and influential international research ethics documents. Launched in 1964, when ethical guidance for research was scarce, the Declaration comprised eleven basic principles and provisions on clinical research. The document has since evolved to a complex set of principles, norms, and directions for action of varying degrees of specificity, ranging from specific rules to broad aspirational statements. It has been revised six times in an effort to maintain its influence. While all revisions were the result of vigorous debate, the 2000 revision and two subsequent notes of clarification spurred particular controversy surrounding the use of placebo in clinical research and the standard of care and post-trial obligations in research in developing countries. Several institutions opted to cite earlier versions of the Declaration, and the U.S. Food and Drug Administration (FDA) recently removed all reference to the Declaration in its approval requirements for drugs and biological products that are studied outside the United States.