The decline in organized violence in the period after World War II provides the promise of a more peaceful future. How can we move further in this direction? Democratic peace—the absence of armed violence between democracies and the domestic peace of mature democracies—may provide part of the answer. This phenomenon is a well-established empirical regularity, but its mechanisms and its limits remain a subject of continuing research. The key role of democracy in reducing violence has been challenged by alternative explanations, such as the liberal peace, the capitalist peace, the developed peace, the organized peace, the quality of government peace, the feminist peace, and the civil society peace—but also by realism. In this essay, part of the roundtable “World Peace (And How We Can Achieve It),” I argue that it is a social-democratic peace that provides the best basis for a lasting world peace. This formula includes democracy but incorporates additional elements, such as a market economy, an active and competent state, close international cooperation, and the reduction of discrimination and group-based inequality. Combining these elements would provide a solid basis for eliminating violence between, as well as within, states. The main limitation of such a program is its demanding nature. Few states and interstate relations as yet fulfill all these conditions, but the long-term trends are moving in the right direction.