Four-component instructional design (4C/ID) is a research-based, prescriptive instructional theory providing guidelines for the teaching of complex cognitive skills and professional competencies. In the early 1990s, it was the first comprehensive instructional design model replacing a part-task approach with a whole-task approach, taking real-life or professional tasks as a starting point for design. Rather than working from part-tasks to the whole task, simple-to-complex versions of the whole task are used to set up the training program. This sustains a process of complex learning in which learners simultaneously develop knowledge, skills, and attitudes. This entry discusses the four components of the model, the development of its psychological basis, and the Ten Steps to Complex Learning.