In the Summa Theologiae, Aquinas offers an adept account of the vice of envy. Despite the virtues of his account, he nevertheless fails to provide an adequatedefinition of the vice. Instead, he offers two different definitions each of which fails to identify what is common to all cases of envy. Here I supplement Aquinas’saccount by providing what I take to be common to all cases of envy. I argue that what is common is a “perception of inferiority”—when a person perceives her ownself-worth to be inferior to another and thereby feels her own self-worth diminish. By incorporating perceptions of inferiority into the definition of envy, we obtain adefinition that retains the spirit of Aquinas’s thought, while improving upon its letter.