A mortgage broker is a middleman who brings mortgage borrowers and lenders together. They help borrowers connect with lenders assessing and recommending the best fit in terms of a borrower's financial situation and interest rate requirements. Traditionally a mortgage broker will gather and review all the paperwork for the mortgage application and pass this on to a lender for underwriting and approval. Most brokers work on a commission basis which means the service is free and they will only get paid by the lender once the loan has been processed.