Developments in contract law over the past century have led to the proliferation of interpretive theories according to which contract law is no longer a sui generisi legal branch. It is widely accepted that if there is a sui generis contractual obligation, it must somehow be based on the wills of the parties. But a new orthodoxy in contract theory claims that the role of the will of the parties in contract law has been progressively shrinking due to judicial doctrines within the law of contract and also to general statutory provisions. It is no longer apparent that there is any interesting sense in which contractual liability is based on the will of the parties. Hence, so it is claimed, contract law has lost its sui generis nature. The article challenges this new orthodoxy. But rather than reverting to the old orthodoxy-the will theory of contracts (or its contemporary rendition, contract as promise)-it argues that we should resist being forced to choose between them. The article argues that the purpose of contractual liability is to support the practice of voluntary obligations. This view preserves an important connection between contractual liability and voluntary undertakings and meets the objections that beset the will theory.