Kay traces its roots to 1890 in Chicago, when the firm that would become Kay Musical Instruments started building mandolins as the Groeschel Company. After passing through the Stromberg-Voisinet name, it was reorganized in 1931 by Henry "Kay" Kuhrmeyer and operated as Kay Musical Instrument Company. From its Chicago factory, Kay produced an enormous range of stringed instruments — acoustic and electric guitars, basses, lap steels, banjos, mandolins, ukuleles, violins, cellos and double basses — and supplied house-branded instruments to retailers and catalog sellers like Sears, Montgomery Ward and Silvertone.

Though often associated with student-grade and budget instruments, Kay also built professional models that became part of mid-century American music. The K-161 "Thin Twin" electric is closely identified with bluesman Jimmy Reed, and the company's late-1950s endorsement deal with jazz guitarist Barney Kessel produced the Jazz Special, Artist and Pro archtops (notably the K6700). Kay upright basses were widely used in jazz, bluegrass and rockabilly. The original Chicago company dissolved in 1968 after being absorbed into Valco, and the Kay name passed through several owners over the following decades.

The brand is now operated by the Kay Guitar Company, which markets a Kay Vintage Reissue line aimed at recreating the look and feel of the 1950s and 1960s instruments. The reissue catalog includes the Thin Twin, the Jazz II thinline archtop, the Barney Kessel signature archtops, and the Pro Bass and Jazz Special Bass, along with reproductions of the company's distinctive "Kelvinator" headstock and art-deco appointments.

Kay has 75 products cataloged on Equipboard, including Semi-Hollowbody Electric Guitars, Solid Body Electric Guitars, and Steel-string Acoustic Guitars. Their gear is featured by 83 artists, with the strongest followings in Rock, Folk, World, & Country, and Blues. Notable users include Frank Iero, Paul McCartney, and Jack White. Kay's catalog spans the full price spectrum — from entry-level options to high-end flagships.