Co-sourcing is a practice of service in a business where a service is performed by staff inside an organization and also by an external service provider. It may be a service performed in relation with a client's existing internal audit department. It may focus on one or more aspects of the internal audit function. Co-sourcing is more advantageous than total outsourcing in a way that it reduces risks, brings in transparency, clarity and better control over the processes outsourced.
An 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.