When the possibility of needing to prove it legally later arises. Do so especially whenever money, goods or services are exchanged and make sure to include dates and amounts. Have a notary public sign it at the bank for a whopping $6 and your butt will be covered.

It should always be in writing, that way you have an concrete understanding and no one can come back later and say, "I didn't say that!".

From a legal standpoint, there are only a few types of contracts that must be written and signed by the parties in order to be legally enforceable. Each state has a "statute of frauds" that lists the types of contracts. With some minor changes, however, the following categories are pretty universal: "[T]he following contracts are invalid, unless they, or some note or memorandum thereof, are in writing and subscribed by the party to be charged or by the party's agent: (1) An agreement that by its terms is not to be performed within a year from the making thereof. (2) A special promise to answer for the debt, default, or miscarriage of another[;] (3) An agreement for the leasing for a longer period than one year, or for the sale of real property, or of an interest therein; such an agreement, if made by an agent of the party sought to be charged, is invalid, unless the authority of the agent is in writing, subscribed by the party sought to be charged. (4) An agreement authorizing or employing an agent, broker, or any other person to purchase or sell real estate, or to lease real estate for a longer period than one year, or to procure, introduce, or find a purchaser or seller of real estate or a lessee or lessor of real estate where the lease is for a longer period than one year, for compensation or a commission. (5) An agreement that by its terms is not to be performed during the lifetime of the promisor. (6) An agreement by a purchaser of real property to pay an indebtedness secured by a mortgage or deed of trust upon the property purchased, unless assumption of the indebtedness by the purchaser is specifically provided for in the conveyance of the property. (7) A contract, promise, undertaking, or commitment to loan money or to grant or extend credit, in an amount greater than one hundred thousand dollars ($100,000), not primarily for personal, family, or household purposes, made by a person engaged in the business of lending or arranging for the lending of money or extending credit." --California Civil Code Section 1624.

In the UK a handshake is an agreed contract protected by law if you have 3 witnesses or more......Good Ye Olde Laws Of Merry England

When ever money or goods and services are to be exchanged you should have a contract. Especially for loans and the sale of property. That way everybody's covered and nobody can back out at the last minute and leave you hoilding the bag.

i know the handshake is and can be legal, you can never go wrong with it in writing!

ANYTIME you have something of VALUE to loose...it is a good idea to have a contract. Value...could be YOUR TIME and SERVICES..REAL ESTATE, OR other transferable property or assets. If whatever IT is...is of a VALUE to you or the other person...I say draw up a contract/agreement of what it is and what each person is responsible for doing with regards to IT.

Always, even between friends and family. Something can always come up and make for a difficult situation. People die, people misunderstand, people forget. Always use contracts, even homemade ones. And get signatures from both parties.

A verbal contract is not worth the paper it's written on.

It should be written in stone every time I allways keep my recipts and have every thing witten and there name signed dated there blood type there bra size personal information. I dont trust an old fashion ok or an hand shake from a used car sales place or any place at all even renting owning you allways need to able to prove every thing these days. photos, cameras, camcorders, recorders,etc.

When you want an easy way to prove it exists.

Always. Otherwise a contract is worthless.

Contracts can be written or oral. Most contracts don't have to be in writing. Buying food or going to the movies are examples of contracts that are not in writing. It's usually better to have a written contract because oral contracts are hard to prove especially without witnesses. There are contracts that must be in writing or the courts will not enforce them.