In this paper I defend and develop Bernard Williams’ claim that the ‘constitutive thought’ of regret is ‘something like “how much better if it had been otherwise”’. An introductory section on cognitivist theories of emotion is followed by a detailed investigation of the concept of ‘agent-regret’ and of the ways in which the ‘constitutive thought’ might be articulated in different situations in which agents acknowledge casual responsibility for bringing about undesirable outcomes. Among problematic cases discussed are those in which agents (...) have caused harm through no fault of their own, or have been constrained to choose the lesser of two evils or to act against their moral values. R. Jay Wallace’s ‘bourgeois predicament’ and related cases, in which we recognize that our present advantages have flowed from regrettable antecedents, further show that regret is often not a simple emotion, and it is argued that conflicted regrets are sometimes unavoidable. Finally, the paper looks at Descartes’ account of regret as a form of sadness engendered by the recollection of irrecoverable happy experiences, to which the ‘constitutive thought’ does not readily apply. It is suggested that what Descartes is discussing is a different genre of emotion for which ‘nostalgia’ might be a better name. (shrink)