These terms refer to a planning method that takes into account all resources available to or required for a given enterprise or activity. "All resources" includes both those owned and controlled by the firm or entity doing the planning, and any additional resources that can be outsourced from other providers. The objective of IRP is to determine the mix of owned/controlled and outsourceable resources that produce to the lowest possible costs. In energy planning, one of the resources used in the process is the input of the general public into the planning process, and in many cases costs include externalities, which are costs borne by the environment or the general public which are not the direct responsibility of an energy producer.

IRP is often misinterpreted in context of the energy industry, since it appears to imply planning in relation to fuel resources or environmental resources. The term is used so often because it is a required planning method in some jurisdictions, and is often essential for compliance with 1992 amendments to the US Clean Air Act.

IRP was used primarily as a least-cost planning strategy in the 1980s and is now used primarily to insure minimal environmental and social impacts. The two terms are now considered synonymous.

See also: