All contracts need to include at least four things to be legal and enforceable:

1. Something needs to be offered (the offer)
2. Something needs to be exchanged for it, usually money, otherwise it is a gift or a promise rather than a contract. (a consideration)
3. Both sides need to accept the terms of the contract (the acceptance)
4. Both sides need to agree to the conditions and understand that they have entered into a contract (mutuality).

Have you been in any situation where these conditions were not met? Please comment.