An indictable conspiracy is an agreement for such a purpose as to render that agreement criminal. The major controversy in conspiracy legal doctrine has involved defining the range of unlawful purposes which are central to an evaluation of liability. The broad view holds that conspiracy exists if the purposes of an agreement are sufficiently reprehensible in general public policy terms, whereas the competing restrictive doctrine confines conspiracy to several well-defined categories, such as conspiracy to commit a crime or to defraud. Lord Denman's antithetical characterization of a conspiratorial agreement as one either to commit an unlawful act or a lawful act by illegal means has been used by courts since the early 1800's to justify broad interpretations of conspiracy. The historical background of the Denman analysis is traced through common law and judicial decisions of the 18th and early 19th centuries which are seemingly compatible with the broad view of conspiracy. It is unclear, however, from the terse language of these rulings if that was their original intent. Although the Denman analysis was criticized in the late 19th century as not being a true test of liability in conspiracy, it continued to play a marginal role in conspiracy cases and achieved new prominence after 1960 when a series of English cases employed a broad, public policy interpretation of conspiracy to find a criminal liability for agreements. An examination of these decisions covers Shaw, Knuller, and Kamarra cases. Australian court decisions which have paralleled most English cases are also reviewed. The 1975 case of D.P.P. v. Withers is examined because it represents a watershed decision restricting conspiracy to specific areas. Categories proposed by jurists which should be included under this doctrine are detailed, such as conspiracy to defraud, to pervert the course of justice, to corrupt public morals, to commit a tort, and to injure a person. Statutory provisions of Australia's States and territories which restrict the liability for conspiracy are described. Finally, the impact of the Law Commission's reforms on England and Australia is assessed. A total of 134 footnotes are included.