This Element explores approaches to spread, scale-up, and sustainability in healthcare improvement. It outlines how these concepts have been defined and operationalised, highlighting areas of ambiguity and contention. The authors focus on three specific approaches: the Dynamic Sustainability Framework, the 3S (structure, strategy, supports) infrastructure approach for scale-up, and the NASSS (non-adoption, abandonment, and challenges to scale-up, spread, and sustainability) framework. Key points are illustrated through empirical case narratives, and the Element concludes with actionable learning for those engaged in improvement activities and for researchers. Spread refers to the adoption of new ways of working by new users, while scale-up involves the extent to which an improvement initiative is adopted more widely within a sector. Sustainability is about maintaining improvements over time. These concepts are often viewed as sequential, but the authors argue that they are inherently overlapping and interdependent processes. They emphasize the need to consider spread, scale-up, and sustainability as adaptive processes in complex systems characterised by uncertainty, unpredictability, and emergence. The authors discuss the importance of balancing fidelity and adaptability in improvement interventions. They highlight the need to consider the sustainability of different aspects, including the sustainability of the intervention itself, the service or health system, and the planet. They also address the time frames for sustainability and the influences on spread, scale-up, and sustainability, including organisational, interorganisational, and external factors. The Element presents three frameworks: the Dynamic Sustainability Framework, the 3S scale-up infrastructure approach, and the NASSS framework. These frameworks provide tools to help manage complexity in spread, scale-up, and sustainability efforts. The Dynamic Sustainability Framework emphasizes ongoing adaptations of improvement interventions over time in their implementation contexts. The 3S approach focuses on developing infrastructure to support widespread implementation of improvement interventions. The NASSS framework aims to understand and explain unpredictability, uncertainty, dynamic interactions, and interdependencies in technology projects. The authors conclude that a combination of approaches is needed to effectively address the complexities of spread, scale-up, and sustainability in healthcare improvement. They emphasize the importance of considering the context, the sustainability of different aspects, and the time frames for sustainability in order to achieve successful and sustainable healthcare improvement.This Element explores approaches to spread, scale-up, and sustainability in healthcare improvement. It outlines how these concepts have been defined and operationalised, highlighting areas of ambiguity and contention. The authors focus on three specific approaches: the Dynamic Sustainability Framework, the 3S (structure, strategy, supports) infrastructure approach for scale-up, and the NASSS (non-adoption, abandonment, and challenges to scale-up, spread, and sustainability) framework. Key points are illustrated through empirical case narratives, and the Element concludes with actionable learning for those engaged in improvement activities and for researchers. Spread refers to the adoption of new ways of working by new users, while scale-up involves the extent to which an improvement initiative is adopted more widely within a sector. Sustainability is about maintaining improvements over time. These concepts are often viewed as sequential, but the authors argue that they are inherently overlapping and interdependent processes. They emphasize the need to consider spread, scale-up, and sustainability as adaptive processes in complex systems characterised by uncertainty, unpredictability, and emergence. The authors discuss the importance of balancing fidelity and adaptability in improvement interventions. They highlight the need to consider the sustainability of different aspects, including the sustainability of the intervention itself, the service or health system, and the planet. They also address the time frames for sustainability and the influences on spread, scale-up, and sustainability, including organisational, interorganisational, and external factors. The Element presents three frameworks: the Dynamic Sustainability Framework, the 3S scale-up infrastructure approach, and the NASSS framework. These frameworks provide tools to help manage complexity in spread, scale-up, and sustainability efforts. The Dynamic Sustainability Framework emphasizes ongoing adaptations of improvement interventions over time in their implementation contexts. The 3S approach focuses on developing infrastructure to support widespread implementation of improvement interventions. The NASSS framework aims to understand and explain unpredictability, uncertainty, dynamic interactions, and interdependencies in technology projects. The authors conclude that a combination of approaches is needed to effectively address the complexities of spread, scale-up, and sustainability in healthcare improvement. They emphasize the importance of considering the context, the sustainability of different aspects, and the time frames for sustainability in order to achieve successful and sustainable healthcare improvement.