Co-sourcing is a business practice where a service is performed by staff from inside an organization and also by an external service provider as a type of auditing.  It can be a service performed in conjunction with a client's existing internal audit department. The scope of work may focus on one or more aspects of the internal audit function.  Co-sourcing earns advantage over Total Outsourcing in a way that it minimizes sourcing risks and brings in transparency, clarity, and better control over the processes outsourced.

Examples of co-sourcingservices are supplementing the in-house internal audit staff with specialized skill, such as information risk management or integrity services; providing routine assistance to in-house auditing for operations and control evaluations in peak period activity; and conducting special projects, such as fraud investigation or plant investment appraisals.  Another example of co-sourcing is outsourcing part of software development or software maintenance activities to an external organization while keeping part of the development in-house.