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 Arizona, as in other states, consideration is a fundamental component of a valid contract. Consideration refers to something of value that is exchanged between the parties involved in the contract. This can be money, goods, services, or a promise to act or refrain from acting. The key aspect is that the consideration must be something that the parties have bargained for; it cannot be a gift or an act that has already been performed. Without this exchange of value, a contract may be deemed unenforceable. However, Arizona recognizes the doctrine of promissory estoppel, which means that if one party makes a promise and the other party relies on that promise to their detriment, the promise may be enforceable even without consideration. This is to prevent injustice due to the relying party's reasonable assumption that the promise would be fulfilled. Lastly, if the consideration is so negligible that it can be considered illusory, the contract may not be enforceable in Arizona because it lacks the substance of a true exchange. Contracts with illusory promises do not have the necessary consideration to be binding.