For over two decades, health services researchers and managers have focused on improving integration between organizations and levels of care. Yet, healthcare systems capable of delivering integrated care have not developed widely. This dissertation argues that structural and process strategies for integration need to be supplemented by attention to the social cognitions that characterize the behaviours of actors within healthcare systems. The aim of this dissertation is to explore how Shared Mental Model Theory might advance our understanding and measurement of integration processes and performance. The first paper in this dissertation examines the evolution of healthcare integration strategies over twenty-five years as reported in the academic literature. Six major, inter-related shifts were identified in strategy content. This evolution in conceptualization and practice highlights the importance of attention to meanings and perceptions. The second paper draws from Shared Mental Model Theory, and an exploratory, theory-driven literature review, to identify mental model content specific to system-level integration efforts, and to develop a theoretical framework of the antecedents, moderators and outcomes of shared mental models of integration. The final paper validates and improves the proposed content framework using a two-round, web-based modified Delphi process with a diverse, pan-Canadian group of integration experts, including policymakers, planners, managers, care providers, educators, researchers and patient advocates. The proposed “Integration Mindsets Framework” may be used to facilitate the planning, implementation, management and evaluation of integration initiatives. A shared mental models lens complements and fills the gaps of current approaches to the study of integration in the healthcare sector by focusing attention on the evolution and interplay of meanings, interpretations and knowledge about integration – and their potential impact on practice. Together, these studies provide theory-based, expert-validated constructs and frameworks that enable researchers and practitioners to describe, conceptualize and analyze health systems integration from a socio-cognitive perspective.