Anthony Joshua vs. Andy Ruiz Jr. was a heavyweight professional boxing match contested between undefeated and unified WBA (Super), IBF, WBO, and IBO champion Anthony Joshua, and former world title challenger Andy Ruiz Jr. The bout took place on June 1, 2019, at Madison Square Garden in New York City, New York. Joshua was originally scheduled to face undefeated WBA No. 2 and WBO No. 3 ranked heavyweight Jarrell Miller, who was replaced by Ruiz Jr. after Miller failed three drug tests.

In boxing, the undisputed champion of a weight class is the boxer who simultaneously holds world titles from all recognized major organisations by each other and the International Boxing Hall of Fame. There are currently four major sanctioning bodies: WBA, WBC, IBF and WBO. There were many undisputed champions before the number of major sanctioning bodies recognizing each other increased to four in 2007, but there have only been 19 boxers to hold all four titles simultaneously.