This innovative Handbook presents a comprehensive overview of the significance of complexity theory for understanding institutions. Eminent scholars analyse the key tools and concepts of the field, including emergence, networks, ergodicity, and modularity, exploring their contributions to institutional formulation and evolution. Bridging the gap between complexity theory and mainstream economics, this pioneering Handbook reveals novel approaches to understanding institutional processes from the micro to the macro level. Chapters balance theoretical discussions with practical analysis, showcasing the relevance of complexity to specific areas such as cities, forests, religion, and historical development. Ultimately, the Handbook argues that viewing economies and societies as co-evolving, non-linear, path-dependent, and non-equilibrium systems can provide invaluable insights into the study of institutional emergence and impact.