A cassette deck is a type of tape machine for playing and recording audio cassettes that does not have a built-in power amplifier or speakers, and serves primarily as a transport. In the 1980s and early 1990s, tape decks were commonly used in vehicle stereo systems, portable cassette players, and home component systems. In the latter case, it is also called a component cassette deck or just a component deck.

The first consumer tape recorder to employ a tape reel permanently housed in a small removable cartridge was the RCA tape cartridge, which appeared in 1958 as a predecessor to the cassette format. At that time, reel-to-reel recorders and players were commonly used by enthusiasts but required large individual reels and tapes which had to be threaded by hand, making them less accessible to the casual consumer. Both RCA and Bell Sound attempted to commercialize the cartridge format, but a few factors stalled adoption, including lower-than-advertised availability of selections in the prerecorded media catalog, delays in production setup, and a stand-alone design that was not considered by audiophiles to be truly hi-fi.

The compact cassette (a Philips trademark) was introduced by the Philips Corporation at the Internationale Funkausstellung Berlin in 1963 and marketed as a device purely intended for portable speech-only dictation machines.^{[citation needed]} The tape width was 1⁄8 inch (actually 0.15 inch, 3.81 mm) and tape speed was 1.875 inches (4.76 cm) per second, giving a decidedly non-Hi-Fi frequency response and quite high noise levels.

Early recorders were intended for dictation and journalists and were typically hand-held battery-powered devices with built-in microphones and automatic gain control on recording. Tape recorder audio-quality had improved by the mid-1970s, and a cassette deck with manual level controls and VU meters became a standard component of home high-fidelity systems. Eventually the reel-to-reel recorder was completely displaced. There were usage constraints due to their large size, along with expense, and the inconvenience of threading and rewinding the tape reels. Cassettes are more portable and can be stopped and immediately removed in the middle of playback without rewinding. Cassettes became extremely popular for automotive and other portable music applications. Although pre-recorded cassettes were widely available, many users would combine (dub) songs from their vinyl records or other cassettes to make a new custom mixtape cassette.

In 1970, the Advent Corporation combined Dolby B noise reduction system with chromium dioxide (CrO₂) tape to create the Advent Model 200, the first high-fidelity cassette deck. Dolby B uses volume companding of high frequencies to boost low-level treble information by up to 9 dB, reducing them (and the hiss) on playback. CrO₂ used different bias and equalization settings to reduce the overall noise level and extend the high-frequency response. Together these allowed a usefully flat frequency response beyond 15 kHz for the first time. This deck was based on a top-loading mechanism by Nakamichi. The follow-on Model 201 was based on a more reliable transport made by Wollensak. Both models featured an unusual single VU meter that could be switched between or for both channels. The Model 200 featured piano key style transport controls, with the Model 201 using the distinctive combination of a separate lever for rewind and fast forward and the large play and stop button as found on Wollensak commercial reel-to-reel machines of the era.

Most manufacturers adopted a standard top-loading format with piano key controls, dual VU meters, and slider level controls. There were then a variety of configurations leading to the next standard format in the late 1970s, which settled on front-loading with cassette well on one side, dual VU meters on the other, and later dual-cassette decks with meters in the middle. Mechanical controls were replaced with electronic push buttons controlling solenoid mechanical actuators, though low-cost models would retain mechanical controls. Some models could search for and count gaps between songs.

Cassette decks soon came into widespread use in applications such as home audio systems, mobile use in cars, as well as portable recorders. From the mid-1970s to the late 1990s the cassette deck was the preferred music source for the automobile. Like an 8-track cartridge, it is relatively insensitive to vehicle motion, but has a smaller physical size and fast forward and rewind capability.

A major boost to the cassette's popularity came with the release of the Sony Walkman personal cassette player in 1979, designed specifically as a headphone-only ultra-compact wearable music source. Although the vast majority of such players eventually sold were not Sony products, the name Walkman has become synonymous with this type of device.^{[citation needed]}