Meaningful and sustained assessment is best achieved when a campus unit takes a collaborative leadership role to work with other departments, offices, and groups. Simply developing and implementing assessment in isolation and for the unit itself is not enough. While the value of collaboration among diverse campus constituents is widely recognized, it is not easily achieved. This occasional paper synthesizes the results of the program Assessment in Action: Academic Libraries and Student Success (AiA) by the Association of College and Research Libraries, which involved over 200 campus teams led by librarians. Five particularly compelling AiA findings are the positive connections documented between various functions of the library and aspects of student learning and success: (1) Students benefit from library instruction in their initial coursework; (2) Library use increases student success; (3) Collaborative academic programs and services involving the library enhance student learning; (4) Information literacy instruction strengthens general education outcomes; and (5) Library research consultations boost student learning. These findings emerged from an assessment process grounded in collaborative planning, decision-making, and implementation. In this paper, we describe the collaborative practices advanced by the AiA program and explain how these practices promote assessment aligned with institutional priorities, encourage common understanding among stakeholder groups about attributes of academic success, produce meaningful measures of student learning, create a unified campus message about student learning and success, and focus on transformative and sustainable change. This paper asserts that the AiA experience serves as a framework for designing assessment approaches that build partnerships and generate results for improving student learning and success through action research, and that the program results demonstrate how libraries contribute to fostering broad student outcomes essential to contemporary postsecondary education. The assessment practices that emerged from the AiA projects can be implemented in a variety of institutional settings and with varying campus priorities. [Foreword by Lisa Janicke Hinchliffe.]