The acrimonious division of American open-wheel racing — often referred to simply as "The Split" — began in 1994 when Tony George announced the formation of the Indy Racing League. The IRL launched its first season in 1996 with a focus on ovals and production-based, less expensive engines, explicitly outlawing the turbocharged CART machinery that had dominated the Indianapolis 500. CART retaliated in 1996 by staging the rival U.S. 500 at Michigan on the same day as the Indy 500.
The schism damaged open-wheel racing's popularity in the United States severely. Top CART teams such as those of Roger Penske and Chip Ganassi eventually crossed over to the IRL in the early 2000s, eroding CART's viability. Champ Car, CART's successor, filed for bankruptcy in February 2008, and a merger agreement was reached by late February, with the combined series running under the IndyCar banner from 2008 onward. The unified series also absorbed the full historical statistics and records of both organizations.
The series was called the Indy Racing League from 1996 to 1999, gaining its first title sponsor as the Pep Boys Indy Racing League in 1998. The name IndyCar Series was officially adopted beginning in 2003 following the expiration of a 1996 legal settlement with CART over the use of the "IndyCar" trademark. Verizon Communications served as title sponsor from 2014 to 2018, followed by Japanese telecommunications company NTT from 2019 onward.
Since its founding, the series has used a single-make chassis formula. Dallara has been the sole chassis supplier since 1997 and won a competitive tender in 2010 to continue in that role. The current Dallara DW12 chassis — named in honor of Dan Wheldon following his fatal crash at Las Vegas in 2011 — was introduced in 2012 and carried the series through to 2026, with an updated universal aero kit introduced in 2018. A successor chassis, initially designated IR-27, was announced in December 2024 and subsequently delayed to a 2028 debut as the IR-28.
Engine competition has varied across the series' history. The opening seasons used a 4.0-litre naturally aspirated V8 formula with Oldsmobile (later Chevrolet), Infiniti, and eventually Toyota and Honda. Honda became the sole engine supplier from 2006 to 2011. From 2012 onward, Chevrolet and Honda have competed with twin-turbocharged 2.2-litre V6 engines producing between 550 and 750 horsepower depending on boost level, with a hybrid energy recovery system introduced from the 2024 season. Firestone has been the exclusive tire supplier since 2000.
Fuel has been another defining characteristic: the IRL used methanol at its inception, switched to an ethanol blend in 2007 — making IndyCar the first major series to run renewable fuel — and has continued with variants of that formula, with Shell supplying 100% ethanol from 2023 onward.
The series began as a pure oval racing series, running at the Indianapolis Motor Speedway, Phoenix, and the short-lived Walt Disney World Speedway. It expanded gradually to include other ovals used by NASCAR before adding road and street courses from 2005, with St. Petersburg the first permanent street event. Following the CART/Champ Car merger, events at Long Beach, Detroit, and Toronto transferred to the IndyCar calendar.
A major turning point came after Dan Wheldon's fatal crash at Las Vegas Motor Speedway in 2011, which led IndyCar to remove 1.5-mile superspeedways from the schedule. From 2012 onward, the calendar has broadly split into one-third oval events, one-third permanent road courses, and one-third temporary street circuits in major cities. The Indianapolis 500 remains the centerpiece of the season each May.
The series' premier event, the Indianapolis 500, was first held in 1911 and has been contested at Indianapolis Motor Speedway ever since, with the exception of 1917–18 (World War I), 1942–45 (World War II), and a date shift to August in 2020 due to the COVID-19 pandemic. The 500 was part of the Formula One World Championship from 1950 to 1960. From 2014 to 2022 it awarded double points in the championship; that practice was discontinued from 2023.
Race winners receive 50 points, with points descending through the field. Bonus points are awarded for pole position (one point), leading at least one lap (one point), and leading the most laps (two points). In the event of a tie in the standings, the driver with the most race victories is declared champion.
The series was carried by ABC and ESPN from 2000 to 2008, then by NBC Sports and affiliated channels from 2009 to 2024. Beginning in 2025, Fox Sports holds the series' U.S. broadcast rights, with all races airing on Fox while supplementary content appears on FS1 and FS2.