The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors and were the CPU of many workstations and high-end personal computers of the time. As the original implementation of the 32-bit extension of the 80286 architecture, the i386 instruction set, programming model, and binary encodings are still the common denominator for all 32-bit x86 processors, which is termed the i386 architecture, x86, or IA-32, depending on context.

The 32-bit i386 can correctly execute most code intended for the earlier 16-bit processors such as 8086 and 80286 that were ubiquitous in early PCs. Over the years, successively newer implementations of the same architecture have become several hundreds of times faster than the original 80386 (and thousands of times faster than the 8086). The 20 MHz version operates 4-5 MIPS. It also performs between 8,000 and 9,000 Dhrystones per second. The 25 MHz 386 version was clocking 7 MIPS. A 33 MHz 80386 was reportedly measured to operate at about 11.4 MIPS.

Development of i386 technology began in 1982 under the internal name of P3. The tape-out of the 80386 development was finalized in July 1985. The 80386 was introduced as pre-production samples for software development workstations in October 1985. Manufacturing of the chips in significant quantities commenced in June 1986, along with the first plug-in device that allowed existing 80286-based computers to be upgraded to the 386, the Translator 386 by American Computer and Peripheral. Mainboards for 80386-based computer systems were cumbersome and expensive at first, but manufacturing was justified upon the 80386's mainstream adoption. The first personal computer to make use of the 80386 was the Deskpro 386, designed and manufactured by Compaq; this marked the first time a fundamental component in the IBM PC compatible de facto standard was updated by a company other than IBM.

In May 2006, Intel announced that i386 production would stop at the end of September 2007. Although it had long been obsolete as a personal computer CPU, Intel and others had continued making the chip for embedded systems. Such systems using an i386 or one of many derivatives are common in aerospace technology and electronic musical instruments, among others. Some mobile phones also used (later fully static CMOS variants of) the i386 processor, such as BlackBerry 950 and Nokia 9000 Communicator. Linux continued to support i386 processors until December 11, 2012, when the kernel cut 386-specific instructions in version 3.8.