The chapter "Approaches to Spread, Scale-Up, and Sustainability" by Chrysanthi Papoutsí, Trisha Greenhalgh, and Sonja Marjanovic explores the challenges and strategies involved in spreading and sustaining improvements in healthcare. The authors review academic and grey literature to define and operationalize the concepts of spread, scale-up, and sustainability, highlighting areas of ambiguity and contention. They discuss three specific approaches: the Dynamic Sustainability Framework, the 3S (structure, strategy, supports) infrastructure approach, and the NASSS (non-adoption, abandonment, and challenges to scale-up, spread, and sustainability) framework. Each approach is examined for its theoretical assumptions and practical implications, with empirical case studies illustrating how different perspectives on spread and scale-up affect implementation in practice. The chapter concludes with actionable lessons for improvement practitioners and researchers to develop sustainable and scalable initiatives. Key points include the need to view spread, scale-up, and sustainability as overlapping and interdependent processes, the importance of balancing fidelity and adaptability, and the role of context in shaping these processes. The chapter also emphasizes the complexity and unpredictability of healthcare improvement efforts, advocating for a systems approach that accounts for ecological factors and the evolving nature of both interventions and contexts.The chapter "Approaches to Spread, Scale-Up, and Sustainability" by Chrysanthi Papoutsí, Trisha Greenhalgh, and Sonja Marjanovic explores the challenges and strategies involved in spreading and sustaining improvements in healthcare. The authors review academic and grey literature to define and operationalize the concepts of spread, scale-up, and sustainability, highlighting areas of ambiguity and contention. They discuss three specific approaches: the Dynamic Sustainability Framework, the 3S (structure, strategy, supports) infrastructure approach, and the NASSS (non-adoption, abandonment, and challenges to scale-up, spread, and sustainability) framework. Each approach is examined for its theoretical assumptions and practical implications, with empirical case studies illustrating how different perspectives on spread and scale-up affect implementation in practice. The chapter concludes with actionable lessons for improvement practitioners and researchers to develop sustainable and scalable initiatives. Key points include the need to view spread, scale-up, and sustainability as overlapping and interdependent processes, the importance of balancing fidelity and adaptability, and the role of context in shaping these processes. The chapter also emphasizes the complexity and unpredictability of healthcare improvement efforts, advocating for a systems approach that accounts for ecological factors and the evolving nature of both interventions and contexts.