Despite growing recognition, definitions of social innovation remain contested, ranging from views that emphasise novelty to those that reduce it to isolated products or events. To promote clarity, a pragmatic and action-oriented definition treats social innovation as a dynamic process of co-creation and transformation shaped by diverse actors and settings. The conceptual framework draws on three key theories—theory of change, institutional theory, and actor–network theory—to map how social innovations emerge, diffuse, and become institutionalised. Each theory offers unique insights into actors’ dynamics, sociotechnical systems, and the dessemination of innovation. In addition, diffusion of innovation explains how innovations scale through networks of early adopters, opinion leaders, and systemic enablers. Measuring the impacts of social innovation requires moving beyond conventional metrics and focusing on processes, long-term shifts, and embedded value. This requires the establishment of a multidimensional framework captures four key domains of impact: institutional development, sociotechnical transformation, environmental sustainability, and cultural change. By aligning theoretical foundations with real-world application, the chapter provides a robust conceptual and evaluative basis for advancing social innovation in diverse contexts.