Ambisonics is a full-sphere surround sound format created by a group of English researchers — among them Michael A. Gerzon, Peter Barnes Fellgett, and John Stuart Wright — under support of the National Research Development Corporation (NRDC) of the United Kingdom. In addition to the horizontal plane, the format incorporates sound sources above and below the listener. The term is used as both a generic name and formerly as a trademark.

Unlike some other multichannel surround formats, its transmission channels do not carry speaker signals. Instead, they contain a speaker-independent representation of a sound field called B-format, which is then decoded to the listener's speaker setup. This extra step allows the producer to think in terms of source directions rather than loudspeaker positions, and offers the listener a considerable degree of flexibility as to the layout and number of speakers used for playback.

Ambisonics was developed in the UK in the 1970s under the auspices of the British National Research Development Corporation.

Despite its solid technical foundation and many advantages, ambisonics had not until recently^[when?] been a commercial success, and survived only in niche applications and among recording enthusiasts.

With the widespread availability of powerful digital signal processing (as opposed to the expensive and error-prone analog circuitry that had to be used during its early years) and the successful market introduction of home theatre surround sound systems since the 1990s, interest in ambisonics among recording engineers, sound designers, composers, media companies, broadcasters and researchers has returned and continues to increase.

In particular, it has proved an effective way to present spatial audio in Virtual Reality applications (e.g. YouTube 360 Video), as the B-Format scene can be rotated to match the user's head orientation, and then be decoded as binaural stereo.

Ambisonics can be understood as a three-dimensional extension of M/S (mid/side) stereo, adding additional difference channels for height and depth. The resulting signal set is called B-format. Its component channels are labelled ${\displaystyle W}$ for the sound pressure (the M in M/S), ${\displaystyle X}$ for the front-minus-back sound pressure gradient, ${\displaystyle Y}$ for left-minus-right (the S in M/S) and ${\displaystyle Z}$ for up-minus-down.

The ${\displaystyle W}$ signal corresponds to an omnidirectional microphone, whereas ${\displaystyle XYZ}$ are the components that would be picked up by figure-of-eight capsules oriented along the three spatial axes.