The Beach Boys' bootleg recordings are recordings of performances by the Beach Boys that attained some level of public circulation without being available as a legal release. Many albums by the band were fully assembled or near completion before being shelved, rejected, or revised as an entirely new project. In recent years, new rarities compilations and reissues of studio albums have been released with studio outtakes included as bonus tracks.

Bootleg recordings arise from a multitude of sources, including broadcast performances, recordings of live shows, test discs, privately distributed copies of demos, and covertly copied studio session tapes. Some recordings have never seen wide public circulation. Others are only rumored to exist, were misapprehended to tangentially related projects, or have yet to surface in the hands of archivists or record collectors. This article includes commonly bootlegged material and unreleased recordings which are reported to exist.

Some of the largest sources of Beach Boys bootleg material has derived from the Pet Sounds and Smile sessions; their underground circulation eventually resulted in the officially-issued compilations The Pet Sounds Sessions (1997) and The Smile Sessions (2011). In 2013, the latter won the Grammy Award for Best Historical Album. In 2011, Uncut voted Smile the number one "greatest bootleg recording of all time". In 2003, Stylus Magazine named the Beach Boys' Smile, Landlocked, Adult Child, and Dennis Wilson's Bambu "A Lost Album Category Unto Themselves".

The current existence of most of the Beach Boys' tape masters was made possible by the fact that the band were in control of their own material. Typically, record labels at the time would possess the multi-tracks, then wipe them once a final master was mixed down. However, a myriad of original multi-track masters have been lost due to various circumstances. Some reported currently missing are:

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