Theories of well-being purport to identify the features of lives, and of intervals within lives, in virtue of which some people are high in well-being and others are low in well-being. They also purport to identify the properties that make some events or states of affairs good for a person and other events or states of affairs bad for a person. This article surveys some of the main theories of well-being, with an emphasis on work published since the turn of (...) the century. (shrink)