ADDIE is an instructional design model developed in 1975 at Florida State University to help create effective training programs. It was adopted by the US military as the primary method for developing training to address the need to train large numbers of people in complex technical tasks. The five phases of the ADDIE model are analysis, design, development, implementation, and evaluation. The model provides a systematic process for designing, developing, and evaluating training to ensure it meets learning objectives and business needs.