The series traces its lineage to the IMSA GT Championship, which ran from 1971 to 1998. Through the late 1990s and into the 2000s, top-level North American sports car racing was divided between the technically ambitious American Le Mans Series and the lower-cost Rolex Sports Car Series, which operated in parallel until a landmark merger.
On 5 September 2012, Grand-Am Road Racing announced a merger with the Braselton-based International Motor Sports Association, combining the Rolex Sports Car Series and the American Le Mans Series into a single championship planned to debut in 2014. SME Branding was selected to develop the identity of the new series. On 8 January 2013, a preliminary class structure was announced: Grand-Am's Daytona Prototype category and IMSA's LMP2 class would merge into a single prototype class, with allowance for the DeltaWing, while GT categories from both series would be consolidated.
The new series was formally revealed on 14 March 2013 at the Chateau Élan Hotel and Conference Center at Sebring International Raceway, two days before the 12 Hours of Sebring. American Le Mans CEO Scott Atherton confirmed the new sanctioning body would carry the IMSA name; the United SportsCar Racing title was announced as a contest entry submitted by Louis Satterlee of Florida.
Tudor became the title sponsor for 2014 and 2015 under the name United SportsCar Championship. On 8 August 2015, WeatherTech was announced as the incoming title sponsor, and the series was renamed the IMSA WeatherTech SportsCar Championship beginning with the 2016 season. Fox Sports 1 held broadcast rights for the initial seasons under a deal signed in August 2013. NBC Sports became the exclusive US broadcaster from 2019, with USA Network replacing NBCSN on cable from 2022.
The championship currently fields four classes. Grand Touring Prototype (GTP), the series flagship introduced in 2023, features cars built to either IMSA's LMDh regulations or the ACO's Le Mans Hypercar regulations, enabling cross-entry with the FIA WEC. Le Mans Prototype 2 (LMP2), introduced as a standalone class in 2019, runs ACO-spec cars from licensed constructors — Oreca, Ligier, Dallara, and Riley-Multimatic — with pro-am driver requirements. GT Daytona Pro (GTD Pro) uses FIA GT3 specifications with no driver rating restrictions, while GT Daytona (GTD) uses identical cars but requires at least one silver or bronze-rated driver per entry.
Former classes include Daytona Prototype International (DPi, 2017–2022), the original combined Prototype class (2014–2018), Prototype Challenge using Oreca FLM09 machinery (2014–2017), LMP3 (2021–2023), and GT Le Mans (GTLM, 2014–2021), which ran ACO GTE-specification cars.
The Michelin Endurance Cup (MEC) is a parallel championship awarding points exclusively at the five endurance rounds: the Rolex 24 at Daytona, the 12 Hours of Sebring, the 6 Hours of Watkins Glen, the SportsCar Endurance Grand Prix, and the Petit Le Mans. Points are distributed at staggered intervals that vary by race length. The cup began in 2014 as the Tequila Patrón North American Endurance Cup before Michelin assumed the title sponsorship in 2019.
The Michelin Pilot Challenge (formerly the Continental Tire Sports Car Challenge) serves as the series' support championship, split into Grand Sport (GS) and Street Tuner (ST) classes for production-based touring cars.
The WeatherTech Championship season opens with the Rolex 24 at Daytona on the final weekend of January and concludes with the Petit Le Mans in early October.
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