MySQL is a relational database management system developed under dual license: General Public License / Commercial License by Oracle Corporation and is considered to be the most popular open source database in the world, and one of the most popular in general together to Oracle and Microsoft SQL Server, all for web development environments.

MySQL was initially developed by MySQL AB (company founded by David Axmark, Allan Larsson, and Michael Widenius). MySQL AB was acquired by Sun Microsystems in 2008, and this in turn was bought by Oracle Corporation in 2010, which had already owned Innobase Oy since 2005, a Finnish company that developed the InnoDB engine for MySQL.

Unlike projects like Apache, where the software is developed by a public community and the code copyright is held by the individual author, MySQL is sponsored by a private company, which owns the copyright to most of the code. This is what makes the aforementioned dual licensing scheme possible. The database is distributed in several versions, a Community, distributed under the GNU General Public License, version, and several Enterprise versions, for those companies that want to incorporate it into proprietary products. The Enterprise versions include additional products or services such as monitoring tools and official technical assistance. In 2009 a fork called MariaDB was created by some developers (including some original MySQL developers) unhappy with the development model and the fact that the same company controls both MySQL and Oracle Database products.

It is developed for the most part in ANSI C and C ++. It is traditionally considered one of the four components of the LAMP and WAMP development stack.

MySQL is used by many large and popular websites, such as Wikipedia, Google (though not for search), Facebook, Twitter, Flickr, and YouTube.