In professional boxing, the lineal championship of a weight class is a notional world championship title. It is initially held at some moment in time by a boxer universally acclaimed as the best in the class. Another boxer can win the lineal championship only by defeating the reigning lineal champion in the ring. The lineal champion is described as "the man who beat the man". There is no single canonical list of lineal champions at any weight class, because there is no agreed method of what to do when the current champion retires or moves to a different weight class.

The concept was developed by boxing fans dissatisfied by the tendency of each of the various sanctioning bodies (WBC, WBA, IBF, etc.) to recognize different champions, and in particular to strip a champion of his title for refusing to fight its top-ranked contender. Prior to the 1970s, this rarely happened; the National Boxing Association (NBA) and the New York State Athletic Commission (NYSAC) sometimes recognized different champions, but there was usually only a short interval before one champion defeated the other. The "lineal championship" is intended as a return to that era. Several top boxers have specified holding the lineal championship as a personal accomplishment (e.g., Mike Tyson & Lennox Lewis) or goal (e.g., Nate Campbell).