A group of indexes made up of 25 tranches of commercial mortgage-backed securities (CMBS), each with different credit ratings. The CMBX indexes are the first attempt at letting participants trade risks that closely resemble the current credit health of the commercial mortgage market by investing in credit default swaps, which put specific interest rate spreads on each risk class. The pricing is based on the spreads themselves rather than on a pricing mechanism.

Daily trading involves cash settlements between the two parties to any transaction, and the CMBX indexes are rolled over every six months to bring in new securities and continuously reflect the current health of the commercial mortgage markets. This "pay as you go" settlement process considers three events in the underlying securities as "credit events": principal writedowns, principal shortfalls (failures to pay on an underlying mortgage) and interest shortfalls (when current cash flows pay less than the CMBX coupon).


|||The introduction of indexes like the CMBX has led to massive growth in the structured finance market, which includes credit default swaps, commercial mortgage-backed securities, collateralized debt obligations and other collateralized securities. Trading in the CMBX tranches is done over the counter, and liquidity is provided by a syndicate of large investment banks.

While the average investor cannot participate in the CMBX indexes directly, they can view current spreads for a given risk class to assess how the market is digesting current market conditions, making it a potentially valuable research tool.