This pedagogical note discusses the differences between second and third-degree price discrimination. The comparison uses four important factors, namely, market segmentation, information about consumers, profit maximization and social welfare. The comparison shows that while market segmentation is a prerequsite for third-degree, it is an equilibrium outcome in second-degree price discrimination. The profit maximization problem is unconstrained under third-degree but it is constrained under second-degree. Both deadweight loss and consumer surplus are positive under third-degree, but they both can be zero under second-degree and the social surplus is maximum.