Constructivists debate the baseline for comparing temporal periods and the relevant units of an international system. Macro-level structural comparisons lend themselves to the study of incremental change in the international system. Exploring manifestations of structure at three levels of analysis, this chapter reviews how scholars use macro-historical comparison, genealogy, and participant observation. The constructivist work on regimes focuses on the characteristics and dynamics of the liberal world economy, often building on Polanyi's analysis of the relationship between property rights, financial institutions, and social purpose in the transition to capitalism in Britain. Recognizing such complexity in the effects of institutional settings, and the interaction between actors and structures in maintaining or changing those institutions, provides a subtler understanding of power in the international system. A cluster of early constructivist work focused on rules and norms, both within and beyond formal organizations, the League of Nations, International Court of Justice, General Agreement on Tariffs and Trade (GATT), and the European Union.