IMCA Modified is the top modified division sanctioned by the International Motor Contest Association. The series began in 1979. It was designed to be a mid-level class between late models and hobby stocks. The first IMCA modified race was held at the Benton County, Iowa Speedway in 1979 on a 1/4 mile track.

The car bodies are hybrids of open wheel cars and stock cars. The front tires have no body around them like an open wheel car, and the back wheels have a body around them like a stock car. The series has an engine claim rule where any driver finishing fourth or lower and on the lead lap may claim a driver who finished ahead of him for a fee (originally $325, but now $1,050, or $100 and an exchange of engines; at the IMCA Super Nationals, the winner's engine is automatically claimed and sold at auction, where proceeds fund the top ten drivers' prize money), and because of the short length of the events, the tires used at the start must be used at the finish of the race ("one tire" rule) from specification supplier Continental AG.

A sport modified division was created out of this division in the mid-2000s. This class features a similar chassis with lower horsepower, with the claim rule being $550. The division is divided into Northern and Southern Modified classes depending on the track's location in the United States. The Northern Modifieds feature restricted motors and chassis. The Southern Modifieds are purpose-built cars on 1978–87 General Motors G-Body chassis.

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