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 Illinois, 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 to a contract. It can be a promise, an act, a benefit, or a forbearance. Illinois law requires that each party to a contract must provide consideration for the agreement to be legally binding. If a contract lacks consideration, it may be deemed unenforceable. However, Illinois 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 Illinois because it lacks the substance of a true exchange. Courts will look at the intention of the parties and the reality of the exchange to determine if a contract is illusory.