One of the central problems in both moral and legal philosophy has been to offer a satisfactory analysis of the concept of obligation. In ordinary language the word "obligation" is used in several different contexts. It may refer to moral obligation (e.g., "I am morally obligated to keep my promise to help my uncle with his knitting"), legal obligation (e.g., "I am legally obligated to report as income on my tax return whatever funds I embezzle from my employer"), political obligation (e.g., "I am politically obligated to vote"), or social obligation (e.g., "I am socially obligated to write a note of thanks to my weekend hosts"). For philosophical purposes the concept must be more sharply delineated. This note will examine H. L. A Hart's analysis of obligation as it is developed in The Concept of Law and in "Legal and Moral Obligations." Two principal criticisms will be suggested. First, either there is an inconsistency between Hart's general characterization of obligation and his characterization of legal obligation in particular, or, if they are consistent, both analyses are unacceptable. It ·will be argued that there are circumstances that Hart would clearly regard as posing legal obligations that do not fall under his general characterization of obligation. Second, if Hart's analyses of legal obligation and of obligation in general are incompatible, it must be his account of the general term "obligation" that is unsatisfactory.