The Cadillac ATS is a compact executive car (D-segment) manufactured by General Motors and marketed by Cadillac from the 2013 to 2019 model years, available in both four-door sedan and two-door coupé body styles. In the US, it is the brand's first locally built entry-level premium car since the Cimarron, and in Europe, it is the successor to the Swedish-built Cadillac BLS. The ATS was developed at the General Motors Technical Center in Warren, Michigan and assembled at the Lansing Grand River Assembly plant in Lansing, Michigan.

Using GM's Alpha platform, the ATS was offered in either rear- or all-wheel drive configurations. The ATS base engine had been a naturally aspirated 2.5-liter I-4 gasoline engine that produces 202 hp (151 kW) (until the 2016 model year). Optional engines include a 2.0-liter turbocharged I-4 gasoline engine that produces 272 hp (203 kW) and a naturally aspirated 3.6-liter V6 gasoline engine that produces 321 hp (239 kW). The 2.0-liter engine replaced the 2.5-liter engine as the base engine for the 2017 model year. All versions were equipped with a 6-speed GM 6L45 Hydra-Matic automatic transmission as standard until the 2015 model year. An 8-speed automatic transmission was introduced for the 2016 model year. The 2.0-liter turbocharged, rear-wheel drive version can be mated to an optional 6-speed Tremec M3L TR-3160 manual transmission.

Prior to the debut of the ATS, Cadillac's smallest vehicle was the E-segment CTS. The CTS was comparable in price to D-segment competitors like the Audi A4, the BMW 3 Series, the Lexus IS and the Mercedes-Benz C-Class, but was comparable in size and weight to the more expensive BMW 5 Series. Although Cadillac believed that customers would favor a Mercedes-Benz E-Class-sized sedan at the price of a 3 Series, this assumption was proven to be incorrect. Cadillac's research found that target customers who already owned vehicles like the 3 Series or A4 did not want a larger vehicle.

Cadillac debuted the ATS to the press in January 2012, before beginning production in July of that year, with sales beginning in August as a 2013 model. Cadillac sold the ATS in the United States, Canada, Mexico, Europe, the Middle East, China, Japan, and South Korea. The ATS was replaced by the Cadillac CT4 in 2019 for the 2020 model year.

Cadillac, upon discovering that the public wanted something small and designed with consideration, began full-scale development of a compact car in 2009, with said car being given the designation "ATS". The ATS was developed by GM engineers working principally at the General Motors Technical Center in Warren, Michigan, United States. In August 2009, vice president of design Edward Welburn revealed a full-size styling buck of the ATS alongside the XTS luxury saloon.

To establish parameters around which they would design the ATS, GM engineers benchmarked the 1999-2006 BMW E46 3 Series, which ATS chief engineer Dave Masch and his team regarded as the most dynamic and driver-focused iteration of the BMW 3 Series. The engineers emphasized low weight when developing the ATS, and their efforts resulted in a finished vehicle that weighed less than the E46 benchmark. To achieve this result, Masch suggested that the engineering team disregard certain GM product development rules that, had they been followed, would have resulted in a heavier vehicle.

During the early development of the ATS, GM engineers determined that downsizing the GM Sigma II platform that underpinned the second-generation CTS would make the car too heavy, and that using an economical, front-wheel drive platform would sacrifice performance expected of a Cadillac sedan. Under the leadership of Dave Leone, GM engineers created a new platform designed to be light and compact, to be capable of handling both rear- and all-wheel drive configurations, and to have a near 50/50 weight distribution. The new platform developed by the GM engineers for the ATS was called the GM Alpha platform.

Cadillac took two years to conclude the development of the ATS. Ken Kelzer, engineering executive for GM, said that it would have been possible to simply cut down a CTS, which would have resulted a "pretty good car". However, he said that since the BMW 3 Series was its direct competitor, a unique platform would be optimal. Larry Craig, the ATS Program Engineering Manager, said that several iterations were completed until a compromise was made between manufacturability, weight and strength. Consequently, the lightest ATS weighed 3,315 lb (1,504 kg), compared to a BMW E46 328i at 3,461 lb (1,570 kg). Dave Leone, vehicle line executive for rear-wheel-drive and performance cars, knew that downsizing the larger CTS would result in a small car not able to deliver the performance wanted in the segment. Leone and his team established a dollar-per-kilogram strategy to measure the cost effectiveness of weight-reduction. The engineers made sure to monitor materials used in developing the ATS, which resulted in an almost perfect weight distribution figure of 51 percent and 49 percent for front and rear, respectively.