Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, the Network File System (NFS), and SPARC microprocessors. Sun contributed significantly to the evolution of several key computing technologies, among them Unix, RISC processors, thin client computing, and virtualized computing. Notable Sun acquisitions include Cray Business Systems Division, Storagetek, and Innotek GmbH, creators of VirtualBox. Sun was founded on February 24, 1982. At its height, the Sun headquarters were in Santa Clara, California (part of Silicon Valley), on the former west campus of the Agnews Developmental Center.

Sun products included computer servers and workstations built on its own RISC-based SPARC processor architecture, as well as on x86-based AMD Opteron and Intel Xeon processors. Sun also developed its own storage systems and a suite of software products, including the Solaris operating system, developer tools, Web infrastructure software, and identity management applications. Technologies included the Java platform and NFS.

In general, Sun was a proponent of open systems, particularly Unix. It was also a major contributor to open-source software, as evidenced by its $1 billion purchase, in 2008, of MySQL, an open-source relational database management system.

At various times, Sun had manufacturing facilities in several locations worldwide, including Newark, California; Hillsboro, Oregon; and Linlithgow, Scotland. However, by the time the company was acquired by Oracle, it had outsourced most manufacturing responsibilities.

On April 20, 2009, it was announced that Oracle Corporation would acquire Sun for US$7.4 billion. The deal was completed on January 27, 2010.