World cities are reaching previously inconceivable sizes and populations, and this escalation of urban quantities and scales has ignited a fascination for the phenomenon of megacities. For the last fifteen years, The Megacities Foundation has encouraged public debate on this development, uniting practitioners from the fields of architecture, economics, geography, sociology and urban planning. This book offers a compilation of the Foundation's best lectures, defining megacities and their processes and systems, and initiating an open-ended public discussion on the evolution, governance and design of these multifaceted, expanding urban territories.