A Credit Support Annex (CSA) is a legal document that regulates credit support (collateral) to mitigate counterparty risk in financial contracts. Effectively, a CSA defines the terms under which collateral is posted or transferred between swap counterparties to mitigate the credit risk arising from in the money derivative positions. It is one of the four parts that make up an ISDA Master Agreement but is not mandatory; it is possible to have an ISDA agreement without a CSA but normally not a CSA without an ISDA.