Separation of mechanism and policy

The separation of mechanism and policy is a design principle in computer science. It states that mechanisms (those parts of a system implementation that control the authorization of operations and the allocation of resources) should not dictate (or overly restrict) the policies according to which decisions are made about which operations to authorize, and which resources to allocate.

This is most commonly discussed in the context of security mechanisms (authentication and authorization), but is actually applicable to a much wider range of resource allocation problems (e.g. CPU scheduling, memory allocation, Quality of Service), and the general question of good object abstraction.