This book provides the first systematic explanation of the origins of constitutional designs from an analytical, historical, and comparative perspective. Based on a comprehensive analysis of constitutional change in Latin America from 1900 to 2008 and four detailed case studies, Gabriel Negretto shows that the main determinants of constitutional choice are the past performance of constitutions in providing effective and legitimate instruments of government and the strategic interests of the actors who have influence over institutional selection. The book explains how governance problems shape the general guidelines for reform, while strategic calculations and power resources affect the selection of specific alternatives of design. It also emphasizes the importance of the events that trigger reform and the designers' level of electoral uncertainty for understanding the relative impact of short-term partisan interests on constitution writing. Negretto's study challenges predominant theories of institutional choice, and paves the way for the development of a new research agenda on institutional change.