A survey of the elementary functions of money and its invariant representations, alongside the complementary topic of ownership. The book uses the language of Promise Theory to explain the semantics and lifecycle of money in a concise and semi-formal manner, with the goal of reaching a modern probabilistic view of money and economics as a network, independent of philosophical or political treatments as well as models that build on Game Theory. Relativistic notions like `value' are distinguished carefully from invariant measures of amount to decouple frequently muddled concepts in the popular literature, and money is distinguished from its many inequivalent representations (i.e. proxy technologies). A key strength of this work lies in the way it exposes money as an interconnection network, which has evolved to communicate intentions and decisions between agents in a network, where prices form a language for information channels that we call markets.This book is aimed at economists, philosophers, and engineers. It introduces readers to the concepts in a practical manner, building on the concept of voluntary cooperation. The book draws on many examples from the real world, with a particular emphasis on semi-formal semantics. 'A must read for anyone involved in designing intelligent digital currency.'--Mike Warner (Senior Strategist, San Francisco Federal Reserve)