The SIG Sauer P320 is a modular semi-automatic pistol made by SIG Sauer, Inc., SIG Sauer's American branch. It is a further development of the SIG Sauer P250, utilizing a striker-fired mechanism in lieu of a double action only hammer system. The P320 can be chambered in 9×19mm Parabellum, .357 SIG, .40 S&W, .45 ACP, and 10mm Auto and can be easily converted from one caliber to another; a change from .357 SIG to .40 S&W requires only a barrel change; a change from 9mm to .357 SIG or .40 S&W is accomplished using a caliber exchange kit.

Several sister companies that design and manufacture firearms use the brand name SIG Sauer. The original company, Schweizerische Waggonfabrik (SWF), later Schweizerische Industrie-Gesellschaft (SIG), went through several selloffs, leaving the SIG Sauer brand spread over several companies. The original SIG is now known as SIG Combibloc Group and no longer has any firearms business.The German company was SIG Sauer GmbH & Co. KG. It was formed in 1976 as a partnership between Schweizerische Industrie Gesellschaft (SIG) of Switzerland and J.P. Sauer & Sohn of Germany. The Swiss company is SIG Sauer AG. Its predecessor SIG Arms AG was sold to L&O Holding in western Germany and was first renamed SAN Swiss Arms AG, commonly known as Swiss Arms, and in late 2019 was further renamed SIG Sauer AG. The American company is SIG Sauer, Inc. Its predecessor SIGARMS was founded in Virginia in 1985 to import and distribute SIG Sauer firearms into the United States: Its headquarters were moved to New Hampshire in 1990. This company was renamed SIG Sauer, Inc. in 2007, and since 2000 is organizationally separate from SIG Sauer GmbH.