One of the most bewildering problems in Muslim law concerns the classification and effect of various types of invalid marriage contract. As in a large number of other such problems, moreover, the conflicting views of the leading jurists and their followers, ancient and modern, are by no means confined to disputes between the recognized Sunni schools (the Hanafis, Malikis, Shafi‘is and Hanbalis), for within the Hanafi school itself the position is no less confu-sing. Some Hanafi jurists, for instance, make a clear distinction between marriage contracts which are irregular (fāsid) and those which are void (bātil), while others use the two words interchangeably. Again, those who make the distinction differ considerably as to which types of invalid marriage contract fall within each category, as to the juristic concepts on which their decision is based, and as to the legal effects involved. The present article represents an attempt to outline the development of Hanafi thought on this matter and thereby to clear up certain common misconceptions.Abu Hanifa himself was relentlessly logical in his approach to this subject, although his logic led him to somewhat strange conclusions. Arguing from the premise that the constituent parts of most contracts are four in number, namely two “considerations” and two contracting parties, he held that if a divine prohibition made either consideration unlawful in nature or either party incompetent to act, then one of the constituent parts of the contract was lacking and the whole vitiated in its very essence: it was therefore void (bāṬil) and of no legal effect, just as though no agreement had been reached between the parties.