This essay is a history of an analogy. It charts a perceived relationship between the Trinity and the conjugal family in Anglo-French lay culture in the later Middle Ages. The association had long been known within theological discussions of the Trinity, antedating the works of St. Augustine, but his disapproving assessment was enduringly to inhibit its use. This essay shows the way that the analogy reemerged in the fourteenth century, bleeding through its theological bandages into debates about the ethics of (...) human relationships. Where this interrelationship has been considered before by medievalists, it has been in criticism of William Langland's Piers Plowman. This essay treats that poem, too, but also maintains that the synergy between marriage and the Trinity was not only the preoccupation of an eccentric poet but had a much more widespread cultural relevance. Indeed, I gather here a range of material, both literature and art, from across Europe between roughly the end of the thirteenth to the mid-fifteenth century; within that evidence, I identify a shared interest in reanimating the apparently exhausted topic of Trinitarianism and the family. (shrink)