Most legal systems contain rules for the exclusion of wrongfully obtained evidence. Clarity is gained by separating three lines of objection to reliance on such evidence in the legal determination of guilt. Each of them is directed at a different institutional actor. The first objection is to the manner in which the police had obtained the evidence; the second is to the use of the evidence by the prosecution to prove its case against the accused or to the inclusion of the evidence in the trial dossier; and the third is to the trial court's reliance on the evidence in finding the accused guilty as charged or, where provision of reasons is required, in supporting that finding. Different theories or rationales for the exclusion of wrongfully obtained evidence have clustered around these three lines of objection. It is usual to find more than one theory or rationale at work in shaping the law. The theoretical exploration is followed by an analysis of legal forms and techniques for exclusion, and a discussion of the major factors that have been treated as relevant in deliberation on exclusion.