An Addendum Agreement is a legal document that amends or adds additional terms, conditions and provisions to an existing contract. This type of agreement is often used to modify one or more sections of the original agreement without having to rewrite the entire contract. It can also be used to change the scope of an existing arrangement or add new parties who must abide by the same requirements as those outlined in the original agreement. The Addendum Agreement should not contradict the original contract’s language but instead should harmonize with it in order to ensure a legally valid document.