Plan B was a Los Angeles–based Eurorack module manufacturer founded by Peter Grenader, a Calarts-trained electroacoustic composer who studied with Morton Subotnick and Barry Schrader. The company was an early advocate of the Eurorack format in the 2000s, helping to popularize the format alongside other small builders before the larger boom that followed.

The brand's modules carried a West Coast design sensibility with a strong Buchla influence, and Plan B's catalog ran across oscillators, function generators, filters, and timbral processors. Notable designs included the triangle-core Model 15 VCO, the Model 13 Timbral Gate (later reissued in limited runs through Electro-Acoustic Research), and the Elf series previewed at NAMM. Grenader also built a one-off custom modular system, the Toolbox Synthesizer, for drummer Danny Carey of Tool.

A selection of Plan B modules was reissued under license by cEvin Key's Subconscious Communications imprint, and Grenader has continued designing modules through Electro-Acoustic Research after the original Plan B label.

Plan B has 6 products cataloged on Equipboard, including Modular Synthesizers. Their gear is featured by 1 artist, with the strongest followings in Electronic. Notable users include Richard Devine.