Commercial Mortgage Backed Securities are, as the title explains, backed by loans which are secured with commercial property, rather than residential. The CMBS market provides liquidity and diversification to many commercial real estate investors, as well as provides ready access to capital for commercial lenders. Most lenders follow the underwriting guidelines set forth in the Commercial Mortgage Securities Association. The basic rule taken from this is that if a loan does not conform to the industry, it cannot be sold on the open market.