The IWGP Heavyweight Championship is a professional wrestling heavyweight championship owned by the New Japan Pro Wrestling (NJPW) promotion. "IWGP" is the acronym of NJPW's governing body, the International Wrestling Grand Prix. The title was introduced on June 12, 1987 in the finals of a IWGP tournament. Being a professional wrestling championship, the title is won as a result of a predetermined outcome.

Throughout the history of the championship, several wrestlers have been forced to relinquish the title due to an inability to participate in title defenses. When a wrestler has been injured or unable to compete for other reasons, tournaments have been held to determine the new champion.

In 2006, Brock Lesnar was stripped of the title for being unable to defend it; however, Lesnar claims he was owed money by NJPW and kept the physical belt. He signed with Antonio Inoki's Inoki Genome Federation (IGF) in 2007, and lost the championship to Kurt Angle on the inaugural broadcast. Angle later lost the belt in a unification match to the NJPW-recognized champion Shinsuke Nakamura in 2008.

The IWGP Heavyweight Championship was a professional wrestling heavyweight championship owned by the Inoki Genome Federation (IGF) promotion. The title shares its name with New Japan Pro Wrestling's (NJPW) IWGP Heavyweight Championship, from which it split due to a decision made by IGF and NJPW founder Antonio Inoki. "IWGP" is the abbreviation of NJPW's fictional governing body, the International Wrestling Grand Prix.

During the title's history, IGF recognized it as the official IWGP Heavyweight Championship, continuing the history of the title after an error made by NJPW in Inoki's eyes. NJPW recognized the title as the IWGP 3rd Belt Championship, a championship that was merely represented by a previous version of the IWGP Heavyweight Championship's title belt. The title was briefly used in the Total Nonstop Action Wrestling (TNA) promotion, which recognized it as the IWGP Heavyweight Championship.

As a professional wrestling championship, the title was won via a scripted ending to a match or awarded to a wrestler because of a storyline. The inaugural champion was Brock Lesnar, who was the reigning IWGP Heavyweight Champion before being stripped of the title due to issues with NJPW. IGF recognized him as the official IWGP Heavyweight Champion afterwards. All title changes occurred at IGF or NJPW-promoted events. There were a total of three reigns among three wrestlers during the title's brief history before being unified with the IWGP Heavyweight Championship.