Loyalty n3 is the catalyst for an enormous amount of admirable human conduct. It is also a desirable virtue: 'in loyalty . . . is the fulfilment of the whole of morality'. n4 It may be justly argued that loyalty grounds more of the principled, honourable and other kinds of non-selfish behaviour in which people engage than does any other moral principle. Curiously, loyalty is almost totally ignored by the law. The area of law in which the principle of loyalty most acutely applies (at least potentially) is family law -- in particular to the concept of marriage. n5 Loyalty is the brussel sprout of the law. Almost everyone recognises [*2] its inherent goodness but few are prepared to make a meal of it. Despite its moral desirability, there are virtually no legal principles that are expressly derived from, or give effect to, the virtue of loyalty. This paper examines the extent to which loyalty should be given legal recognition in matrimonial law. Although the main purpose of this paper is to raise awareness of the potential relevance of loyalty to the dissolution of marriage (and therefore to encourage further consideration and debate on this issue), for the sake of completeness we provide an example of a legal framework in which loyalty should be incorporated into matrimonial law. We argue that within the scope of the 'no-fault' based system of divorce in some circumstances betrayals should be penalised by means of a reduced property settlement.