An Industry Standard Architecture bus (ISA bus) is a computer bus that allows additional expansion cards to be connected to a computer's motherboard. It is a standard bus architecture for IBM compatibles. Introduced in 1981, the ISA bus was designed to support the Intel 8088 microprocessor for IBM’s first-generation PC.

In the late 1990s the faster peripheral component interconnect (PCI). Soon afterwards, use of the ISA bus began to diminish, and most IBM motherboards were designed with PCI slots. Although there are still a few motherboards being made with ISA slots, these are generally referred to as the legacy bus motherboards.