Most regulations and guidelines require that potential research participants be told a great deal of information during the consent process. Many of these documents, and most of the scholars who consider the consent process, assume that all this information must be disclosed because it must all be understood. However, a wide range of studies surveying apparently competent participants in clinical trials around the world show that many do not understand key aspects of what they have been told. The standard view of the conditions for valid consent therefore implies that these people have failed to give valid consent to research participation. In this paper we argue that the standard view is false. The primary function of the requirement that researchers disclose information about a study is the avoidance of illegitimate control over someone’s consent decision, which is a form of fraud.We derive the content and manner of appropriate disclosure by analysing the ways in which the manipulation of information can invalidate consent. Our analysis shows that the informational requirements for valid consent are conceptually distinct and thus unlikely to have identical contents. This implies that consent can be valid when not everything that ought to be disclosed by the person asking for consent is understood by the person who proffers it.