HDMI (High-Definition Multimedia Interface) is an interface standard used for audiovisual equipment such as high-definition television and home theater systems. With 19 wires wrapped in a single cable that resembles a USB wire, HDMI is able to carry a bandwidth of 5 Gbps (gigabits per second). This is more than twice the bandwidth needed to transmit multi-channel audio and video, future-proofing HDMI for some time to come. This and several other factors make HDMI much more desirable than its predecessors, component video, S-Video and composite video.

HDMI is an uncompressed, all-digital signal, while the aforementioned interfaces are all analog. With an analog interface, a clean digital source is translated into less precise analog, sent to the television, then converted back to a digital signal to display on screen. At each translation, the digital signal loses integrity, resulting in some distortion of picture quality. HDMI preserves the source signal, eliminating analog conversion to deliver the sharpest, richest picture possible.

Previous video interfaces required separate audio cables, with the vast majority of people using standard RCA L/R analog audio jacks. HDMI, with its abundant bandwidth and speed, carries not only video but also up to eight digital audio channels for uncompromised surround-sound. It replaces the tangle of wires behind the system with a single cable, greatly simplifying the entire setup process of the home theater system while delivering top tier performance.

Though standard HDMI or "Type A" has 19 wires, "Type B" will have 29 wires. The latter is targeted for the motion picture industry and other professional applications. Both varieties are "Intelligent HDMI," referring to the built-in capability for HDMI-enabled components to talk to each other via the interface. Auxiliary information can provide all-in-one remote functionality and other interoperable features not possible in previous interface technologies.

HDMI supports standard video formats, enhanced video and high-definition. It is also backwards compatible with DVI (Digital Video Interface). High-end graphics cards featuring a DVI port can connect to a HDMI interface via a DVI/HDMI cable. This is simply a cable with a DVI connector on one end and a HDMI connector on the other. As a rule, HDMI cables should not run longer than 15 feet (5 meters), or degradation of the signal could occur.

As of 2005, many high-end television sets were sold with at least one HDMI interface. Some experts advise that two HDMI interfaces will provide more flexibility, and for those who want to connect a game console, three might serve better. Multiple interfaces will become common on digital TVs as the industry incorporates HDMI interfaces into more peripheral components.