How do innovations diffuse in societies and organizations? It is an interesting yet a complex question to answer. In order to shed some lights on this fundamental question, this book chapter provides the foundations of diffusion of innovations theory along with two empirical cases.

The theory is discussed through a three-component model of diffusion: innovation, sources and adopters. It mainly builds upon the seminal work of the well-known sociologist and communication scholar, Everett Rogers (1962).

The empirical cases are based on diffusion of solar photovoltaic (PV) systems. The first case is about off-grid solar PV systems in Bangladesh, while the second case is about on-grid solar PV systems in Germany.Overall, the differences and similarities between the two case studies in developing and developed countries let us explain how the characteristics of innovation, sources and adopters affect the diffusion of innovations.