This paper examines the historical and theoretical basis of the privilege against self-incrimination and the case-law regarding the privilege before the UK and European courts in order to understand better the development of the privilege in relation to competition investigations in the UK and EU. The historical and theoretical basis of the privilege indicates that the privilege is a relatively modern legal creation and a number of theoretical bases are offered to justify its existence. The theoretical justifications assist in a better understanding of the extant case-law, but indicate that some of the distinctions drawn between categories of protected information have no clear basis. The paper goes on to examine the difference between self-incrimination and self-accusation, the extension of ‘human’ rights to corporate entities, and the existence of a privilege as a ‘functional necessity’. Finally the paper makes some suggestions about the type of information that might be sought legitimately in competition investigations and those requests that might be challenged.