This document discusses theories and models of instructional system design. It begins by defining instructional design and describing it as a systematic process involving teaching methods, learners, materials, and the learning environment to achieve learning goals. It then covers various learning theories that influence instructional design like behaviorism, cognitivism, and constructivism. Specific instructional design models are also summarized like the ADDIE model, Gagne's nine events of instruction, and macro vs micro level models. The document emphasizes that there is no single best approach and the design must consider the unique objectives and audience.