Consideration may be thought of as the concept of value offered and accepted by people or organisations entering into contracts. Anything of value promised by one party to the other when making a contract can be treated as "consideration": for example, if A signs a contract to buy a car from B for $5,000, A's consideration is the $5,000, and B's consideration is the car.

In common law it is a prerequisite that both parties offer consideration before a contract can be thought of as binding. The doctrine of consideration is irrelevant in many jurisdictions, although contemporary commercial litigant relations have held the relationship between a promise and a deed is a reflection of the nature of contractual considerations. If there is no element of consideration found, there is thus no contract formed.

There are a number of common issues as to whether consideration exists in a contract. Under English law:

Additionally, under the Indian Contract Act 1872, any consideration is invalid if it is:

The most noticeable distinction between the English and Indian criteria for consideration is that English law prohibits past consideration while Indian law does not.

The prime example of this sub-issue is where an uncle gives his thirteen-year-old nephew (a resident of the state of New York) the following offer: "if you do not smoke cigarettes or drink alcohol until your 18th birthday, then I will pay you $5,000". On the nephew's 18th birthday, he tells the uncle to pay up, and the uncle does not pay. In the subsequent lawsuit, the uncle wins, because the nephew, by U.S. criminal law, already had a duty to refrain from smoking cigarettes while under 18 and from drinking alcohol while under age 21.

The same applies if the consideration is a performance for which the parties had previously contracted. For example, A agrees to paint B's house for $500, but halfway through the job A tells B that he will not finish unless B increases the payment to $750. If B agrees, and A then finishes the job, B still only needs to pay A the $500 originally agreed to, because A was already contractually obligated to paint the house for that amount.

Contracts where a legally valueless term is bundled with a term that does have legal value are still generally enforceable.

An exception to this rule is where there is a duty owed to a third party. An act done before the giving of a promise to make a payment or to confer some other benefit can sometimes be consideration for the promise. For this to hold, three conditions must be satisfied (Pao On v Lau Yiu Long [1980]):

Suppose A is a movie script writer and B runs a movie production company. A says to B, "buy my script." B says "How about this – I will pay you $5,000 so that you do not let anyone else produce your movie until one year from now. If I do produce your movie in that year, then I will give you another $50,000, and no one else can produce it. If I do not produce your movie in that year, then you're free to go." If the two subsequently get into a dispute, the issue of whether a contract exists is answered. B had an option contract—he could decide to produce the script, or not. B's consideration passed was the $5,000 down, and the possibility of $50,000. A's consideration passed was the exclusive rights to the movie script for at least one year.