An unenforceable contract or transaction is one that's valid, but which the court won't enforce. Unenforceable is usually used in contradistinction to void (or void ab initio) and voidable. If the parties perform the agreement, it'll be valid, but the court won't compel them if they do not. An example of a transaction which is an unenforceable contract is a contract for prostitution under English law. Prostitution isn't actually a crime under English law, Although both soliciting a prostitute a… (More on Unenforceable)