Policy change in various conceptualizations represents a central research interest of comparative policy analysis. This chapter introduces the different conceptualizations of policy change and ways of operationalizing this phenomenon in one specific policy domain, namely environmental protection. The authors present and discuss three different conceptualizations of policy change: the multi-dimensional approach put forward by Hall (1993) and modifications of it, the budget approach by Baumgartner and Jones (1993), and the diffusion approach (Walker 1969). The first approach offers a nuanced understanding of policy change and produces differentiated measurements, whereas the second approach concentrates on patterns of policy change and facilitates the analysis of large amounts of data. The third approach is different from the previous two to the extent that it is interested in one specific form of policy change (i.e. policy innovations) only, that is, the first-time adoption of a policy innovation. Considering that environmental policy is a comparatively recent policy domain, the diffusion perspective is particularly valuable for the analysis of environmental policy change. Each of these conceptualizations has strengths and weaknesses. When choosing among the different conceptualizations both theoretical and practical considerations concerning data availability need to be taken into account. The authors show that an integration of the individual approaches is feasible and could be rewarding to advance the state of research in the study of policy change.