The will is formed through intelligence, through the process in which the human being makes decisions freely and in them legal acts are created, within which we highlight contracts. In the field of law, the person, by means of the agreement of wills, expresses the consent, through the word, the deed or the technology, to celebrate different contracts, in which there are obligations to give or to do, not to do, depending on the contract in that we meet. Every person when entering into a contract must be free from the defects of consent, be it error, intent, bad faith, violence, disability or injury. And as a consequence, rights and obligations will be produced for both contractors, acting in the field of law in a conscious and free way. The interpretation seeks to unravel the meaning of what is stated in a contract, so it will be necessary to go to the letter, that is to say, the textual expression and in case of doubt to the intention of the contracting parties.