Consideration in contract law is the value or benefit given by each party in exchange for the other party’s value or benefit—such as money in exchange for products or services, or mutual promises exchanged. Consideration is often referred to as the bargained-for exchange in which one consideration is exchanged for another consideration.

A mere promise to do or refrain from doing something that lacks consideration in the form of a value or benefit provided by the other party (a return promise) is not a contract and is generally not enforceable. One exception to this rule may be if one party promises to do or refrain from doing something, and the second party relies on that promise to its detriment (by spending money, for example), the detrimental reliance may create an enforceable contract.

And if the consideration for a contract is so insubstantial that it is worthless, the contract is said to be illusory and is not enforceable.

In California, consideration is a fundamental component of a valid contract. It refers to something of value, such as money, services, or a promise, that is exchanged between parties. Each party must provide consideration for the contract to be legally binding. If a promise is made without consideration, it typically cannot be enforced as a contract. However, California recognizes the doctrine of promissory estoppel, which means that if a party relies on a promise to their detriment, the promise may be enforceable even without consideration. This is to prevent injustice due to the relying party's reasonable reliance on the promise. Contracts with consideration that is deemed to be 'illusory' or so insignificant as to be without value, may be considered unenforceable in California because they lack the necessary element of a bargained-for exchange. The concept of consideration and its exceptions are outlined in the California Civil Code and case law, which provide the legal framework for determining the enforceability of contracts.