On 25 January 2026, after twenty-four hours of racing, more than six and a half of them run under neutralisation because of fog, the No. 7 Porsche 963 of Felipe Nasr, Julien Andlauer and Laurin Heinrich won the Rolex 24 at Daytona by a second and a half from the No. 31 Cadillac. For Porsche Penske Motorsport it was a third straight win in the race that opens every IMSA season.

For many European readers the acronym means little. The short answer is that IMSA is the body that runs the championship in which car manufacturers fight it out with prototypes and GT cars on North American circuits. The longer answer explains why it is worth knowing for any brand with an eye on the United States.

In short

• The International Motor Sports Association was founded in 1969 and today runs the IMSA WeatherTech SportsCar Championship, North America’s leading championship for prototypes and GT cars.
• There are four classes: GTP, LMP2, GTD PRO and GTD, which all race together in the endurance events.
• In 2026 the GTP title went to Jack Aitken in Action Express Racing’s No. 31 Cadillac.

What IMSA is

IMSA stands for International Motor Sports Association, the body based in Daytona Beach, Florida, that writes the rules and organises North America’s main sports car races. Its premier championship is called the IMSA WeatherTech SportsCar Championship: a season that runs from January to October and alternates endurance races, such as the 24 Hours of Daytona and the 12 Hours of Sebring, with shorter races on street and permanent circuits.

What strikes first-time viewers is how very different cars share the track. The manufacturers’ hybrid prototypes race alongside GT cars derived from production models, with separate classifications and the same finish line. Every pass between one class and another is a small problem to solve, and in a twenty-four-hour race there are a great many of them.

From 1969 to a single championship

IMSA was founded in 1969 by John Bishop, a former executive of the Sports Car Club of America, and his wife Peggy, with the backing of Bill France Sr., the founder of NASCAR. In the 1970s its GT championship expanded into endurance racing and, from 1973, also included the 12 Hours of Sebring.

For many years American sports car racing was split between two series: Grand-Am, linked to the NASCAR world, and the American Le Mans Series, founded in 1999 by Don Panoz on the rulebook of the ACO, the organisation that runs the 24 Hours of Le Mans. In September 2012 Panoz sold his series to Grand-Am and the merger was announced; in 2013 the new championship got its name and title sponsor, and on 25 and 26 January 2014, at Daytona, the Tudor United SportsCar Championship made its debut. Since 2016 it has carried its current name, with WeatherTech as title sponsor: a deal that began as a ten-year agreement and has already been extended to 2030.

The IMSA classes: GTP, LMP2, GTD PRO and GTD

The top class is GTP (Grand Touring Prototype), introduced in 2023 with the hybrid prototypes of the LMDh rules: the chassis comes from one of four approved LMP2 constructors, the hybrid system is the same for everyone, and the engine and bodywork belong to the brand. In 2026 eleven cars from five makes took part: the Acura ARX-06, BMW M Hybrid V8, Cadillac V-Series.R, Porsche 963 and Aston Martin Valkyrie, the latter built to the Hypercar rules of the World Endurance Championship. Cadillac, BMW and Aston Martin also race the same cars in the World Endurance Championship (WEC), and the chance to use one car in two championships is one of the reasons that brought manufacturers into this class.

LMP2 is the class of simpler prototypes, today in practice all ORECA 07s with Gibson engines, where professionals race alongside non-professional drivers: the 2026 title went to Alex Quinn and George Kurtz, co-founder and chief executive of CrowdStrike, in the No. 04 ORECA of CrowdStrike by APR.

The two GT classes use the same cars, built to the FIA GT3 regulations. GTD PRO is for all-professional line-ups; in GTD the line-ups are mixed, with professional and non-professional drivers. In 2026 GTD PRO was won by Neil Verhagen and Connor De Phillippi in Paul Miller Racing’s No. 1 BMW M4 GT3 EVO, and GTD by Russell Ward and Philip Ellis in Winward Racing’s Mercedes-AMG, their third title in a row.

The races that matter

Four events make up the history of the championship. The Rolex 24 At Daytona, at the end of January, is the season opener and the most famous, run partly on the banking of Daytona International Speedway. The 12 Hours of Sebring, in March, is held in Florida on a former military airfield, with a bumpy surface that is part of its fame. The Six Hours of Watkins Glen, in New York State, is run on one of America’s most historic circuits. Petit Le Mans, at Road Atlanta, closes the season in early October: in 2026 it took place on 3 October and was won by the No. 6 Porsche of Laurens Vanthoor, Kevin Estre and Matt Campbell, just over a second ahead of the BMW.

The official names already say a lot about the commercial model: Rolex 24 At Daytona, Mobil 1 Twelve Hours of Sebring, Sahlen’s Six Hours of The Glen, Motul Petit Le Mans. Every major race has a brand in its title, just like the championship itself.

IMSA in 2026

The 2026 season belonged to Cadillac. Jack Aitken won the GTP drivers’ title in Action Express Racing’s No. 31 Cadillac, which he shared with Earl Bamber and Frederik Vesti; the team won the teams’ title and Cadillac the manufacturers’ crown, its fifth in the top class since 2017. Porsche Penske Motorsport opened and closed the year by winning at Daytona and at Petit Le Mans.

It was also, at least for now, Acura’s last season in GTP: the brand paused its programme with Meyer Shank Racing at the end of 2026, shifting its effort to IndyCar. For 2027 BMW, Cadillac and Porsche have confirmed their presence and there are expected to be four manufacturers in GTP; according to industry reports, Genesis, Ford and McLaren will not arrive, if they do at all, before 2028.

What IMSA offers a company

The first point is the market. IMSA is the main gateway to the United States for anyone working with endurance racing, and its audience can also be reached on television: for 2026 NBC Sports scheduled more than 160 hours of live coverage across NBC, Peacock and NBCSN, races and qualifying included.

The second is variety. A championship with four classes, from the factory GTP cars to the privateer GTD teams, offers very different entry levels, and the brands that have understood this come from every sector: from technology, like CrowdStrike, to lubricants, from watches to car accessories. The naming formula, from the championship down to individual races, shows how much IMSA thinks like a commercial property before it thinks like a sporting body. Michelin, the sole tyre supplier, renewed its agreement in October 2025.

In our view, the value for a European company lies above all in the connection with the rest of motorsport. Several GTP cars, and often the same drivers, also appear in the WEC and at the 24 Hours of Le Mans, so a project built in IMSA can continue in Europe, and vice versa. Anyone looking at the United States also has other routes, from IndyCar to NASCAR, with very different audiences and costs: the choice depends on who you want to reach, not on how famous the series is. For those starting from Europe, our guide on what sets the WEC apart from the 24 Hours of Le Mans is also useful.