INCOSE has been bedeviled by arguments about the definition of systems engineering. Many definitions have appeared, but the only one that is widely accepted is so broad as to be almost a tautology. As a result, INCOSE has been unable to answer many questions in a way that most members can accept.This paper claims that systems engineering can be defined in a way that leads to clean answers to many questions. This definition claims that what people have been calling “systems engineering” can be split into three basic implementations or types of systems engineering: Discovery, a discipline or specialist type that involves significant analysis, particularly of the problem space; Program Systems Engineering, a coordination or generalist type that emphasizes the solution space and technical and human interfaces; and Approach, a process type that can (and should) be performed by any engineer. Such a breakout resolves controversies and has implications on systems engineering training, research, processes, standards, and promulgation.