There has been a significant and growing interest, and growing empirical research, around Public Service Motivation (PSM) in recent years. There are few critiques of the construct, and none from a rationalist perspective. Given that the origins of PSM lie in attempts by public administration scholars to counter rationalist explanations of bureaucratic behavior, this lack of countercriticism is surprising. This article provides a rationalist critique of PSM. It argues that PSM is consistent with, and not an alternative to, rationalist understandings of what motivates individuals. It also argues that a significant gap in the PSM literature is around how civil servants and others make decisions; decisions about the public interest, and thus how and when to allocate public resources. It concludes that seeing PSM as consistent with rationality, and specifically as a form of expressive interests, answers many of the remaining questions about PSM and addresses the substantive gaps in the construct.