Tenneco (formerly Tenneco Automotive and originally Tennessee Gas Transmission Company) is an American Fortune 500 company that has been publicly traded on the NYSE since November 5, 1999 under the symbol TEN. Tenneco, with headquarters in Lake Forest, Illinois, United States is an automotive components original equipment manufacturer and an after-market ride-control and emissions products. In 2011 it reported a revenue of $7.2 billion.

Tenneco, Inc.'s origin was in the Chicago Corporation, established about 1930. Tennessee Gas and Transmission Company (completely separate) had been formed in 1940.

A shortage of fuel for World War II defense industries in the Appalachian area developed when industrial production was increased. The nuclear development operations of the Manhattan Project at Oak Ridge, Tennessee consumed huge quantities of Tennessee Valley Authority electrical power that would have otherwise been available to other industrial operations. The Chicago Corporation was able to acquire a Federal Power Commission (FPC) license to build a pipeline from Texas to Appalachia, eventually expanding to the largest natural gas pipeline network in the United States. These pipelines were acquired by El Paso Corporation in 1996, and are now owned by Kinder Morgan and others.

In the 1950s, the company acquired existing oil companies, including Sterling Oil, Del-Key Petroleum, and Bay Petroleum. The Tennessee division of the Chicago Corporation acquired Tennessee Gas Transmission Company in 1943 to build a natural-gas pipeline 1,265 miles (2,036 km) from Texas to West Virginia. The first line was completed in October 1944. It was followed by three additional pipelines totaling 3,840 miles (6,180 km) during the next 15 years which provide gas to New York and New Jersey.

In 1966, Tennessee Gas was incorporated as Tenneco, Inc. Tenneco expanded into a number of business ventures as a result of diversification. Tenneco bought Houston Oil & Minerals Corporation in the late 1970s. Tenneco owned and operated a large number of gasoline service stations, but all were closed or replaced with other brands by the mid-1990s.

In the 1970s, Tenneco purchased 53% of J.I. Case when they purchased its owner Kern County Land Company, the agricultural equipment manufacturer based in Racine, Wisconsin, USA. In 1972, Tenneco purchased UK-based David Brown Tractors Ltd. and merged it with the J.I. Case business. In 1984, Case parent Tenneco bought selected assets of the International Harvester agriculture division and merged it with J.I. Case. All agriculture products are first labeled Case International and later Case IH. Tenneco purchased the articulated 4WD manufacturer Steiger Tractor in 1986, and merged it into Case IH.

The corporate direction was to buy failing companies, and work to develop them into market leaders. This worked well with Newport News Shipbuilding, but failed miserably with the various tractor companies, probably due in large part to the economy at the time. By 1988, the company was losing $2 million per day. After being pressured by the banks, it was decided to sell off the oil business. Tenneco Oil Exploration Company was split up and sold off to multiple buyers.

By 1994, Tenneco decided to begin getting out of the ag business and agreed to sell 35% of the now named Case Corporation. In 1996, the spin-off of Case Corporation was completed. The company was acquired by Fiat in 1999 and merged with New Holland Agriculture to form CNH Global.

Tenneco Inc. emerged from a conglomerate consisting of six unrelated businesses: shipbuilding, packaging, farm and construction equipment, gas transmission, automotive, and chemicals. The automotive division was spun off from Tenneco, Inc. in 1991 along with the packaging, energy, natural gas, and shipbuilding divisions. All businesses except automotive and packaging were disposed of between 1994 and 1996 (through public offerings, sales, spin-offs and mergers). In 1999, Tenneco Packaging was spun off and renamed to Packaging Corporation of America (Pactiv Corporation).

Since the 1960s Tenneco Automotive sold mufflers (UK: silencers) in Europe, including through the chain "Pit Stop" in Germany. The group bought a German factory in Virnheim in 1969, Swedish Starla in 1974 and French Bellanger and English Harmo Industries in 1976 and Danish Lydex in 1978. More acquisitions followed.

On October 28, 2005 the name was changed from Tenneco Automotive to Tenneco.

Tenneco (under the Tenneco Automotive name) sponsored CART's Detroit Grand Prix from 1999 until the race's cancellation after 2001.

Tenneco is a multi-national corporation with 93 manufacturing facilities in 26 countries located on 6 continents, with major centers of operations in North America, Europe, Australia and Asia. There were 30,000 employees in 2016. The North American manufacturing facilities are located in Arkansas, Illinois, Indiana, Michigan, Missouri, Tennessee, Georgia and Ohio; the corporate headquarters is located in Lake Forest, Illinois, European facilities in Belgium, Poland, Czech Republic, Germany, UK, France, Spain and Portugal, with headquarters located in Belgium, Asian facilities include in India, China, Singapore and Japan, Australian Facilities are in Sydney, Morea (New Zealand) and Clovelly Park and African Facility includes South Africa's Port Elizabeth.

Tenneco owns the following brands:

These are sold to over 500 after-market customers including retailers and wholesalers and to more than 25 OEMs, including Audi, Chrysler, Daimler, Enfield, Fiat, Ford Motor Company, General Motors, Honda, Navistar International, Jaguar Cars, Mahindra & Mahindra, Maruti Suzuki, Mazda, Mitsubishi, Nissan, Porsche, PSA Peugeot Citroën, Renault, Škoda, Suzuki, Tata, Toyota, TVS, Volkswagen Group, Volvo, E-Z-GO, and CLUB CAR.