Koss Corporation is an American company that designs and manufactures headphones. Headquartered in Milwaukee, Wisconsin since 1958, the company invented the first high fidelity stereophones. Koss continues to design and manufacture headphones and audio accessories.

John C. Koss founded the J.C. Koss Hospital Television Rental Company in 1953. After a short time Koss was looking for new ideas, and partnered with Martin Lange to eventually develop a stereo headphone. Based in Milwaukee, Wisconsin, United States, in 1991 Koss Audio & Video Electronics started producing and selling consumer electronics products as a separate company in Hazelwood, Missouri, United States. The Koss family owns more than 75% of the firm.

Having only a high-school education, John C. Koss worked with Lange, an engineer, to develop the headphone that launched the company almost by accident, as they came upon the headphone idea as a result of an attempt to market a portable phonograph. What made this product unique was the privacy switch feature, which gave listeners the opportunity to listen to the first Koss SP/3 Stereophones. Initially, the products purpose was to demonstrate to consumers the high-fidelity stereo sound of the portable phonograph.

Prior to this time, headphones had only been used for communications purposes. In 1958, the design was debuted at a hi-fi trade show in Milwaukee, and audiences were approving of the design. Soon after the trade show, Koss went into business manufacturing and marketing stereophones from his basement apartment. The technology was imitated by competing manufacturers, which set the design and aesthetics of headphones for years to come.

Working out of two nearby locations in the early 1970s - one housing Koss TV-Rental, which also did electronics and musical instrument repairs - and their main facility two blocks to the east - Koss pioneered the high-end "electro-static" "ES series" headphone market. These headphones set the standard for wide-range frequency response. Being very durable, they required service for wear and tear on cords and ear pads - and K&M Electronics (Klenworth & Midwest based in Minneapolis), working out of the TV Rental location, supported the repair efforts, mainly of headphones that came in by the case from those customer locations. Koss headphones were easy and cost-effective to repair. At this site, in a separate garage setup, the musical instrument and electronics repair was done. The TV-rental and repair site was managed by John's brother Pete Koss. Eventually Koss dominated the headphone market, competing mainly with Telex. Koss however was considered a higher quality unit at the time, offering a wide line of models. Growth in the late 1970s caused them to move to their present location on the north side of Milwaukee.

Diversification into related electronics areas in the 1980s ended in disaster for Koss, who filed for bankruptcy protection after a net loss in 1984 of $6 million. Koss emerged from Chapter 11 bankruptcy proceedings in 1985.

In 1991 Michael J. Koss, son of founder John C. Koss, took over as president and chief executive officer.

In December 2009, former vice president of finance Sujata "Sue" Sachdeva was charged in federal court with wire fraud after the firm discovered her embezzlement of $34 million. Sachdeva was sentenced to 11 years in federal prison. Koss was forced to restate five years of financials.

In addition to selling headphones under their own brand, Koss headphones were also rebranded as Radio Shack headphones under license and sold in Radio Shack stores. Some of their more popular products are the Koss Plug and Koss Spark Plug which are noise isolation earphones. Their ability to be adapted to take the high-end Etymotic ear tip (known as the Koss Hybrid), and the popular Koss Porta Pro has contributed to their success. Their budget-priced headphones (the KSC series in particular) are widely regarded as some of the best low-end headphones on the market. Since 1989, all headphones manufactured in North America by KOSS come with a limited lifetime warranty, which covers normal use by the initial user or purchaser.