Wind turbines have become a mainstream technology, a first choice for many when investing in new electricity generation facilities. This comparative case study addresses how governmental policy has been formulated to support the wind turbine innovation and diffusion process. Three innovation stages and corresponding innovation strategies are identified. The first stage is the early movers of the 1970s and early 1980s, including pioneer countries such as Denmark, the United States, Germany, and the Netherlands. The second stage is the booming markets of the 1990s, guided by the successful Danish innovation path of the 1980s. The third stage is the emerging markets of the 1990s and 2000s, including countries such as India and China. Within these different stages, common elements in government policy strategies can be identified as essential for a sustainable and successful innovation process. These can be summarised as: • support diversity in technology and market formation • research, development and demonstration (R,D&D) is necessary but not sufficient • quality assurance is essential for new technologies • support interaction and networking • ensure support is stable, continuous and flexible Taken together, these elements of a successful innovation approach show that government policy needs to support the development of the entire innovation system: not just the development of turbines and associated infrastructure, but also the involvement of actors, networks, and market institutions. The case of wind energy development in Denmark presents a good example of how and why such a systemic approach can succeed.