The mass production of compact audio cassettes began in 1964 in Hannover, Germany. Prerecorded music cassettes (also known as Musicassettes; M.C. for short) were launched in Europe in late 1965. The Mercury Record Company, a U.S. affiliate of Philips, introduced M.C. to the U.S. in July 1966. The initial offering consisted of 49 titles  However, the system had been initially designed for dictation and portable use, with the audio quality of early players not well suited for music. Some early models also had unreliable mechanical design. In 1971 the Advent Corporation introduced their Model 201 tape deck that combined Dolby type B noise reduction and chromium dioxide (CrO2) tape, with a commercial-grade tape transport mechanism supplied by the Wollensak camera division of 3M Corporation. This resulted in the format being taken more seriously for musical use, and started the era of high fidelity cassettes and players.
During the 1980s, the cassette's popularity grew further as a result of portable pocket recorders and hi-fi players such as Sony's Walkman, which used a body not much larger than the cassette tape itself, with mechanical keys on one side, or electronic buttons or display on the face. Sony even made the WM-10 which was smaller than the cassette itself and expanded to hold and play a cassette.
Like the transistor radio in the 1950s and 1960s, the portable CD player in the 1990s, and the MP3 player in the 2000s, the Walkman defined the portable music market in the 1980s, with cassette sales overtaking those ofLPs. Total vinyl record sales remained higher well into the 1980s due to greater sales of singles, althoughcassette singles achieved popularity for a period in the 1990s.
Apart from the purely technical advances cassettes brought, they also served as catalysts for social change. Their durability and ease of copying helped bring underground rock and punk music behind the Iron Curtain, creating a foothold for Western culture among the younger generations. For similar reasons, cassettes became popular in developing nations.
One of the most famous political uses of cassette tapes was the dissemination of sermons by the Ayatollah Khomeini throughout Iran before the 1979 Iranian Revolution, in which Khomeini urged the overthrow of the regime of the Shah, Mohammad Reza Pahlavi.
In 1970s India, they were blamed for bringing unwanted secular influences into traditionally religious areas. Cassette technology was a booming market for pop music in India, drawing criticism from conservatives while at the same time creating a huge market for legitimate recording companies and pirated tapes. In some countries, particularly in the developing countries, cassettes still remain the dominant medium for purchasing and listening to music