This chapter examines the ways in which criminal law treats conspiracies. Some of the controversies examined include: whether it is necessary and/or desirable to criminalize conspiracies; the extent to which there can be a conspiracy under the Criminal Law Act 1977 if the parties have only agreed to commit the substantive offence subject to some condition; what must be agreed and who must intend what to happen for a crime of conspiracy; the mens rea of statutory conspiracies; and whether common law conspiracies are so vague as to infringe the rule of law.