The IBM System i is IBM's previous generation of midrange computer systems for IBM i users, and was subsequently replaced by the IBM Power Systems in April 2008.

The platform was first introduced as the AS/400 on June 21, 1988 and later renamed to the eServer iSeries in 2000. As part of IBM's Systems branding initiative in 2006, it was again renamed to System i. The codename of the AS/400 project was "Silver Lake", named for the lake in downtown Rochester, MN, where development of the system took place.

In April 2008, IBM announced its integration with the System p platform. The unified product line is called IBM Power Systems and features support for the IBM i (previously known as i5/OS or OS/400), AIX and Linux operating systems. Power4 or older hardware ran OS/400 exclusively.

The IBM System/38 was introduced in November 1980 as a minicomputer for general business and departmental use. It was replaced by the AS/400 midrange computer in 1988 which was rebranded as the eServer iSeries in 2000 (in accordance with IBM's new eServer initiative). Later in 2006 it was renamed the IBM System i which lasted until April 2008 (almost 20 years after being introduced) when it too was—finally—replaced by the IBM Power Systems line.