The ADDIE Model is one of many approaches (see also Instructional Systems Design) used by instructional designers and content developers for the purpose of creating instructional course materials. The model has been adopted as the standard approach by many instructional designers because of its flexibility. ADDIE is a five phase process of which each phase is interrelated, and can take place sequentially or concurrently. The five phases are: analysis, design, development, implementation and evaluation. Also see Rapid Application Development.