This article considers the principles that underlie the claim that some contracts are unconscionable and that such contracts should not be enforceable. It argues that it is much more difficult to explain unconscionability than is often supposed, particularly in cases where the contract is mutually advantageous or Pareto superior. Among other things, the article considers whether unconscionability is a defect in process or result, whether the gains in an unconscionable contract are disproportionate, whether there is a strong link between the use of standard forms and unconscionability, and whether the principle of inequality of bargaining power can account for unconscionability. After rejecting several standard explanations of unconscionability, I consider several alternative ways in which it might be explained.