Does a contract have to be in writing to be valid?

A contract can be formed orally. If both parties intend to be bound, there's certainty as to what the obligations on both ends are, and they both agree, a contract is formed, even if it isn't in writing. 

But some contracts have to be in writing, like a contract for real property or a mortgage. Another example is a payday loan — if it isn’t in writing, it isn’t valid.

Otherwise, having a contract in writing is more helpful in terms of evidence. So, for example, if one side doesn't live up to their agreement, the other can point to the written contract to say, hey, you messed up here and I could be owed damages. If it's just oral, then it's harder to prove the underlying obligation.

Check out our primer on contracts here for more info.