The MultiMediaCard, officially abbreviated as MMC, is a memory card standard used for solid-state storage. Unveiled in 1997 by SanDisk and Siemens, MMC is based on a surface-contact low pin-count serial interface using a single memory stack substrate assembly, and is therefore much smaller than earlier systems based on high pin-count parallel interfaces using traditional surface-mount assembly such as CompactFlash. Both products were initially introduced using SanDisk NOR-based flash technology. MMC is about the size of a postage stamp: 32 mm × 24 mm × 1.4 mm. MMC originally used a 1-bit serial interface, but newer versions of the specification allow transfers of 4 or 8 bits at a time. MMC can be used in many devices that can use Secure Digital (SD) cards.

Typically, an MMC operates as a storage medium for devices, in a form that can easily be removed for access by a PC via a connected MMC reader. Modern computers, both laptops and desktops, often have SD slots, which can additionally read MMCs if the operating system drivers can.

MMCs may be available in sizes up to 16 gigabytes (GB). They are used in almost every context in which memory cards are used, like cellular phones, digital audio players, digital cameras, and PDAs. Since the introduction of SD cards, few companies build MMC slots into their devices (an exception is some mobile devices like the Nokia 9300 communicator in 2004, where the smaller size of the MMC is a benefit), but the slightly thinner, pin-compatible MMCs can be used in almost any device that can use SD cards if the software/firmware on the device is capable.

While few companies build MMC slots into devices as of 2018, due to SD cards dominating the memory card market, the embedded MMC (e.MMC) is still widely used in consumer electronics as a primary means of integrated storage and boot ROM in portable devices. eMMC provides a low-cost flash-memory system with a built-in controller that can reside inside an Android or Windows phone or in a low-cost PC and can appear to its host as a bootable device, in lieu of a more expensive form of solid-state storage, such as a traditional NVMe solid-state drive, UFS chip, or SD card.

The latest version of the eMMC standard (JESD84-B51) by JEDEC is version 5.1A, released January 2019, with speeds (250 MB/s read, 125 MB/s write) rivaling discrete SATA-based SSDs (400 MB/s).