an assignment of trust deed is a document that lenders use when they sell loans secured by trust deeds. when a lender in a state like california uses trust deeds instead of mortgages, there’s actually a third party involved. when you sign your loan agreement, called a promissory note, you agree to let your bank take your house if you don’t make your payments. the trust deed is a document that puts the legal ownership of your house in a trust held by a third party trustee. once you make your final payment, the trustee takes the title of the property out of trust and transfers it to you, free and clear of the loan.