The value-form or form of value (German: Wertform) is a concept in Karl Marx's critique of political economy and in Marxist theory. It refers to the social form (a socially attributed status) of a commodity (any product traded in markets), which contrasts with the tangible use-value or practical utility (its "useful form" or "natural form") which it has, as a product which satisfies some human need. Marx calls the commodity form, as a form of value, "the economic cell-form of bourgeois society", meaning it is the simplest economic unit out of which capitalist civilization is built up. He then seeks to provide a brief morphology of the category of economic value as such, with regard to its substance, the forms which this substance takes, and how its magnitude is determined or expressed. He does this in the first instance by analyzing the meaning of the value-relationship that exists between two quantities of commodities.
The "forms of value" of commodities are only the first of a series of social forms which Marx analyzes in Das Kapital, such as the forms of money, the forms of capital, the forms of wages, and the forms of profit. In his dialectical story, each of these forms is shown to grow out of (or "transform" into) other forms, and so all the forms are connected with each other, step by step, logically and historically. At the end, all the forms appear seamlessly integrated with each other in a self-reproducing, constantly expanding capitalist system, of which the distant historical origin has become hidden and obscure; the fully developed system appears other than it really is, and does not transparently disclose its real nature.
Marx borrowed the idea of the form of value from the Greek philosopher Aristotle (circa 360–370 BC), who pondered the nature of exchange value in chapter 5 of Book 5 in his Nicomachean Ethics. However, Marx criticized and developed Aristotle's idea in an original way. In so doing, Marx was also influenced by, and responding to, the classical political economy discourse about the economic laws governing commodity values and money, beginning with William Petty's Quantulumcunque Concerning Money (1682) and culminating with David Ricardo's Principles of Political Economy and Taxation (1817). In particular, Marx's ideas about the forms of value were influenced by Samuel Bailey's criticism of Ricardo's theory of value.