A PCI Mezzanine Card or PMC is a printed circuit board assembly manufactured to the IEEE P1386.1 standard. This standard combines the electrical characteristics of the PCI bus with the mechanical dimensions of the Common Mezzanine Card or CMC format (IEEE 1386 standard).

A mezzanine connector connects two parallel printed circuit boards in a stacking configuration. Many mezzanine connector styles are commercially available for this purpose, however PMC mezzanine applications usually use the 1.0 mm pitch 64 pin connector described in IEEE 1386.

A PMC can have up to four 64-pin bus connectors. The first two ("P1" and "P2") are used for 32 bit PCI signals, a third ("P3") is needed for 64 bit PCI signals. An additional bus connector ("P4") can be used for non-specified I/O signals. In addition, arbitrary connectors can be supplied on the front panel of the chassis or case; also known as a "bezel".

The PMC standard defines which connector pins are used for which PCI signals; in addition it defines the optional 64 "P4" connector pins for use of arbitrary I/O signals.

It enables manufacturers to offer products that are compatible with the well-established PCI bus, but in a smaller and more robust package than standard PCI plug-in cards. The word mezzanine, derived from the Italian mezzanino and also commonly used to refer to a platform inserted between two floors of a building, describes the way in which a PMC fits between two adjacent host cards in a standard card rack, attached to one of the cards by connectors and mounting pillars. A single PMC measures 74 mm x 149 mm. The standard also defines a double-sized card, but this is rarely used.

Carrier cards that accept PMCs are usually made in the Eurocard format, which includes single, double and triple-height VMEbus cards, CompactPCI (cPCI) cards and more recently, VPX cards. One PMC fits on a standard 3U carrier card while 6U models (typical for VMEbus cards) can carry up to two PMCs. PMCs were also used in early ATCA systems prior to the advent of the Advanced Mezzanine Card or AMC.

For the PMC standard, I/O technologies account for much of the market, but various card functions are commercially available including Intel architecture and PowerPC processors, graphics cards, and memory cards. I/O cards are available such as serial communication controllers, SCSI controllers, graphics controllers and FireWire controllers.