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The rich history of blinding in clinical trials spans a couple of centuries.1 Most researchers worldwide appreciate its meaning. Unfortunately, beyond that general appreciation lurks confusion. Terms such as single-blind, double-blind, and triple-blind mean different things to different people.2 Moreover, many medical researchers confuse the term blinding with allocation concealment. The fact that such confusion arises suggests that both terms are misunderstood. Clear theoretical and practical differences separate the two. Blinding prevents ascertainment bias and protects the sequence after allocation.3,4 By contrast, researchers use methods of allocation concealment primarily to prevent selection bias and to protect an assignment sequence before and until allocation. Furthermore, in some trials, blinding cannot be successfully implemented, whereas allocation conceal-ment can always be successfully implemented.4,5 Blinding represents an important, distinct aspect of randomised controlled trials.3 The term blinding refers to keeping trial participants, investigators (usually health-care providers), or assessors (those collecting outcome data) unaware of an assigned intervention, so that they are not influenced by that knowledge. Blinding prevents bias at several stages of a trial, although its relevance varies according to circumstance. Although initial forays into blinding might have used a blindfold,1 the processes have now become much more elaborate. In this article, we focus on the attributes and benefits of blinding. Potential effects of blinding If participants are not blinded, knowledge of group assignment can affect responses to the interventio