Spontaneous Order brings together Peyton Young's research on evolutionary game theory and its diverse applications across a wide range of academic disciplines, including economics, sociology, philosophy, biology, computer science, and engineering. Enhanced with an introductory essay and commentaries, the book pulls together the author's work thematically to provide a valuable resource for scholars of economic theory. Young argues that equilibrium behaviors often coalesce from the interactions and experiences of many dispersed individuals acting with fragmentary knowledge of the world, rather than (as is often assumed in economics) from the actions of fully rational agents with commonly held beliefs. The author presents a unified and rigorous account of how such 'bottom-up' evolutionary processes work, using recent advances in stochastic dynamical systems theory. This analytical framework illuminates how social norms and institutions evolve, how social and technical innovations spread in society, and how these processes depend on adaptive learning behavior by human subjects.