This book provides a comprehensive overview of historical and international debates on the theory of “labor money� or “labor notes.� These debates exist in a triangular context of market socialism, communism (community-based socialism), and local currency, joining numerous socialists, anarchists, and Marx and Engels. Labor note theory encompasses theoretical, ideological, and practical doctrines aimed at designing a fair and desirable labor-based market or non-market economy by reforming the monetary and credit system. This theory was considered an unfeasible utopian idea in the context of orthodox Marxism, which is typically based on a historical study of surplus value doctrines. However, this book eschews Marx critique of “labor money� that limits the debate regarding a concrete alternative society, and instead proposes practical and gradual approaches to social reform by scrutinizing the primary sources of labor money theories and practical experiences and reconstructs their theoretical relationships.