The primary purpose of requiring source code escrow in a contractual agreement is to ensure the source code is available. Source code escrow is a service that involves depositing the source code of a software or system with a third-party agent or escrow provider, who can release it to a designated beneficiary under specific conditions, such as bankruptcy, termination, or breach of contract by the software vendor or developer. Source code escrow can help to protect the interests and rights of the software user or licensee, who may need access to the source code for maintenance, modification, enhancement, or troubleshooting purposes. The IS auditor should verify that the contractual agreement specifies the terms and conditions for source code escrow, such as the escrow agent,the escrow fees, the deposit frequency and format,the release events and procedures, and the verification and audit requirements. References: CISA ReviewManual (Digital Version)1, Chapter 3, Section 3.2.2