4. The investment bank groups the mortgage with similar mortgages it has already purchased (referred to as pooling the mortgages). The mortgages in the pool have common characteristics (similar interest rates, maturities, etc.). The investment bank then prepares for sale securities that represent an interest in the pool of mortgages, of which the homebuyer’s mortgage is a small part (called securitising the pool). The products for sale are called mortgage-backed securities (MBSs).