As much of nonprofit management research on inter-organizational collaboration has focused on various macro and meso aspects of collaboration, little is known about micro aspects such as the attitudes of individuals involved in collaboration. To contribute to a more holistic and multidisciplinary understanding of collaboration, this study draws upon social psychological theories about attitude structure and attitudinal ambivalence to explore the variation in attitudes that nonprofit leaders have toward collaboration opportunities. Based on interviews with the leaders of 20 US-based transnational nonprofits in the field of child welfare, the study qualitatively identifies four major types of attitudes toward collaboration opportunities: Avid, Averse, Apprehensive, and Apathetic. The study then presents several propositions to facilitate a future research program for the integration of attitudes into collaboration research. Practical policy and managerial implications are also discussed.