Examining the legal history of the order to pay money initiating a funds transfer, the author tracks basic principles of modern law to those that governed the payment order of Antiquity and the Middle Ages. Exploring the legal nature of the payment order and its underpinning in light of contemporary institutions and payment mechanisms, the book traces the evolution of money, payment mechanisms and the law that governs them, from developments in Ancient Mesopotamia, Ancient Greece, Rome, and Greco-Roman Egypt, through medieval Europe and post-medieval England. Doctrine is examined in Jewish, Islamic, Roman, common and civil laws. Investigating such diverse legal systems and doctrines at the intersection of laws governing bank deposits, obligations, the assignment of debts, and negotiable instruments, the author identifies the common denominator for the evolving legal principles and speculates on possible reciprocity. At the same time he challenges the idea of 'law merchant' as a mercantile creation. The book provides an account of the evolution of payment law as a distinct cohesive body of legal doctrine applicable to funds transfers. It shows how principles of law developed in tandem with the evolution of banking and in response to changing circumstances and proposes a redefinition of 'law merchant'. The author points to deposit banking and emerging technologies as embodying a great potential for future non-cash payment system growth. However, he recommends caution in predicting both the future of deposit banking and the overall impact of technology. At the same time he expresses confidence in the durability of legal doctrine to continue to evolve and accommodate future payment system developments.