Evaluation is used for two major purposes: internal decision making and communication with the external environment. An organization may need very different approaches and strategies for these two. Much of the work that has been done in library evaluation has been for internal purposes. Evaluation is also important for an organization's relationship with the environment that provides the resources the organization needs to survive. A manager must convince the environment that the organization's mission and goals are of value to the parent organization's larger mission and that the organization is capable of achieving them.