Get to grips with assumption agreements. This simple guide explains their purpose, key elements, and how they affect your business dealings.In real estate transactions, an assumption agreement allows a third party to "assume" or take over the loan of the property's seller. A person who assumes a mortgage takes over a payment from the previous homeowner. An Assumption Agreement is a legal document through which one party transfers its obligations or duties under a contract to another party. It allows one party to "assume" the rights and responsibilities of the other party. An assignment and assumption agreement is a contract that allows one of the parties to transfer their contractual rights and duties to another party. An assumption clause in a mortgage contract allows a home's seller to pass responsibility for the existing mortgage to the new homebuyer.