ABSTRACT AN EXPLORATION OF COLLABORATION AND ORGANIZATIONAL EFFECTIVENESS IN DENVER COUNTY HUMAN SERVICE NONPROFIT ORGANIZATIONS Jane F. Hansberry, PhD University of Pittsburgh, 2005 This study looked at the role of human service organizations' collaboration against the backdrop of the sometimes conflicting influences of New Public Management, the New Federalism, and PRWORA (welfare reform). The study examined the influence of Denver County human service nonprofit organizations' collaborative activities on the organizations' effectiveness. In order to understand collaboration's relative impact on organizational effectiveness, other organizational effectiveness factors measured in the study included management procedures, board of director performance, and change management. The study used a cross-sectional survey and focus groups to gather data. Using survey data from 143 Denver County human service nonprofit organizations and a series of focus groups comprising nonprofit managers and funders, it was found that human service nonprofit organizations are collaborating more now than five years ago. Respondents reported that mission fulfillment is the primary reason for their collaborations, though funding opportunities are also a factor. Other findings are that change management and collaboration are stronger influences on organizational effectiveness than management procedures and board performance. It was found that smaller organizations are more likely to collaborate and that collaboration is a stronger influence on smaller organizations' effectiveness. Focus group results indicate a perception gap between nonprofit practitioners and funders about the level of collaborative activity within the Denver nonprofit community. Implications are discussed that include the need for dialogue in the nonprofit sector about collaboration, better measurement of collaborative activities, and training for nonprofit organizations in collaboration's principles and smart practices.