This article presents a diachronic perspective for implementation research. It analyzes implementation practices in relation to their changing institutional context. Therefore, a comparison is made between different styles of implementation. The relationship between implementation practices and institutional context is analyzed as a structuration process, following Giddens’s theory. Four styles of policy implementation are distinguished: a traditional, bureaucratic, professional, and managerial style. These four styles are connected with different phases in the development of the welfare state. This developmental model is illustrated with an analysis of policy implementation in Dutch public assistance between 1950 and the early 1990s.