The existing literature addressing antecedents of public service motivation (PSM) focuses on personal predisposition and institutional shaping. The authors offer a focus that differs from previous studies, arguing that workplace trust as a result of human interaction and personal choice has a bearing on PSM. It is postulated that public managers' trust in citizens, trust in colleagues, and trust in agency leaders enhance their PSM. The authors test this proposition by using data collected from middle managers working in the Taiwan central government and it receives strong support. This study brings trust into the study of PSM, facilitates interdisciplinary dialogues, and thus helps make PSM a type of knowledge that pushes back the boundaries of public administration.