The Sega Mega Drive is a 16-bit video game console released by Sega in Japan in 1988, North America in 1989, and the PAL region in 1990. It was sold under the name Sega Genesis in North America as Sega was unable to secure legal rights to the Mega Drive name in that region.

The Mega Drive was the successor to the Sega Master System and was Sega's third home console and second to be sold outside of Japan.

The Mega Drive is part of the fourth generation era of consoles, and the first of its generation to achieve notable market share in Europe and North America. It was the direct competitor of the Super Nintendo, although the Sega Mega Drive was released two years earlier. The Sega Mega Drive began production in Japan in 1988 and ended with the last new game being released in 2002 in Brazil.

Although the Sega Master System had proved a success in Brazil and Europe, it failed to ignite much interest in the North American or Japanese markets, which, by the mid-to-late 1980s, were both dominated by Nintendo's large market shares. Meanwhile in the arcades, the Sega System 16 became a success. Hayao Nakayama, Sega's CEO at the time, decided to make its new home system utilize a similar 16-bit architecture. The final design was eventually also used in the Mega-Tech, Mega-Play and System-C arcade machines. Any game made for the Mega Drive hardware could easily be ported to these systems.

The first name Sega considered for its console was the MK-1601, but it ultimately decided to call it the "Sega Mega Drive". Sega used the name Mega Drive for the Japanese, European, Asian, Australian and Brazilian versions of the console. The North American version went by the name "Genesis" due to a trademark dispute, while the South Korean versions were called Super Gam*Boy and Super Aladdin Boy. The Korean consoles were licensed and distributed by Samsung Electronics.

The Mega Drive was released in Japan on October 29, 1988 for ¥21,000, almost exactly a year after the NEC PC Engine. Although this initially caused slow sales, the Mega Drive soon eclipsed the earlier machine in popularity and sales.

In 1987, Sega announced a North American release date for the system (under the name of Sega Genesis) of January 9, 1989, making it the second console to feature a 16-bit CPU (the first one being the Mattel Intellivision) and the first to feature single-instruction 32-bit arithmetic. Sega was not able to meet the initial release date and U.S. sales began on August 14, 1989 in New York City and Los Angeles with a suggested retail price of US$200 at launch. The Genesis was released in the rest of North America on September 15 of the same year with the price reduced slightly to $190.

The European release was on 30 November 1990. In the United Kingdom and Republic of Ireland it was priced at £189.99. The first UK shipment of 30,000 units was sold at retailers Comet, Dixons, Rumbelows and Toys "R" Us. Following on from the European success of the Sega Master System, the Mega Drive became a very popular console in Europe. Unlike in other regions where the NES had been the dominant platform, Sega's marketing strategy was not aimed at direct competition with Nintendo's aging machine. In the United Kingdom the most well known of Sega's advertising slogans was "To be this good takes AGES, to be this good takes SEGA". Some of these adverts employed adult humour and innuendo with sentences like "The more you play with it, the harder it gets" displayed with an illustration of the waggling of a joystick. A prominent figure in the European marketing was the "Sega Pirate". This character was a talking one-eyed skull that starred in many TV adverts with a generally aggressive and humorous attitude. The relatively late release of the Mega Drive in Europe assured a strong launch line-up in comparison with other regions. The arcade ports of classics like Altered Beast, Golden Axe and Ghouls 'n Ghosts, available in stores at launch, provided a strong image of the console's power when compared to other home conversions of these games. The arrival of Sonic the Hedgehog in 1991 was just as successful as in North America, with the new Sega mascot becoming popular throughout the continent.

The Mega Drive was released by Tec Toy in 1990, only a year after the Brazilian release of the Sega Master System. Tec Toy also released the internet service Mega Net, and made exclusive games including a port of Duke Nukem 3D. The Mega Drive is still manufactured in Brazil, with many games built into the console. The last Brazilian title released was Show do Milhão Volume 2, in 2002.

Aside from the release of the Mega-CD (Sega CD in North America) and 32X add-ons for the Mega Drive, Sega's last big announcement came in the form of a partnership with Time Warner in the U.S. to offer a subscription-based service called Sega Channel that would allow subscribers to "download" games on a month-by-month basis. The poor performances of the Mega-CD and 32X, a lack of effective advertising, and disputes between Sega of America and Sega of Japan had taken their toll on the company. By mid 1994, Sega's market share had dropped from 65% to 46%, and the official announcements of newer, more powerful consoles, such as the Sega Saturn, PlayStation, and Nintendo 64 signaled that the 16-bit era was drawing to a close. The last commercial licensed release in North America was Frogger, released by Majesco in 1998.

The Mega Drive was supported until 1996 in Europe until Sega announced they were dropping support for it. It was discontinued along with its predecessor, the successful and long-lived Sega Master System, to allow Sega to concentrate on their next console, the Saturn. The Mega Drive's add-ons, the Mega CD and 32x, were also both discontinued at this point, having been the same general failures they were in the other regions. The last commercial licensed release in Europe was FIFA '98: Road To World Cup, released by Electronic Arts in November 1997. In the UK the last stocks of the Mega Drive II were sold by the end of 1999, Argos selling it with one controller and Mega Games 6 for £24.99.

On May 22, 2006, Super Fighter Team released Beggar Prince, a game translated from a 1996 Taiwanese original. It is the first commercial Sega Mega Drive game since 1998 in the North American market. It was released worldwide.