The increasing popularity of interorganizational collaboration among human services nonprofits has generated significant interest and research from a variety of disciplines. However, the current literature has not sufficiently addressed the factors that shape trust and communication in human services nonprofit partnerships. As such, this study proposes that partner selection shapes trust and communication and, using data on 202 human services nonprofit partnerships in the state of Illinois, examines the relationship between partner selection factors and communication and trust in human services nonprofit partnerships. The results from the hierarchical regression analyses suggest that two partner selection factors, reputation and homophily, are significantly positively related to trust. Regarding the factors that shape communication, the results suggest that prior experience and trust are significantly positively related to communicative effectiveness.