Siel (Società Industrie Elettroniche) was an Italian electronic instrument manufacturer founded in 1976 in the Marche region by a group of former Farfisa employees. The company built electronic organs and analog synthesizers through the late 1970s and 1980s, becoming one of the defining names in the wave of Italian-made synths from that era.

Among its most recognized instruments are the Orchestra string synthesizer (1979), which was rebranded and sold by ARP as the Quartet; the Cruise (1981), a combined mono/poly synth with a built-in string section; and the Opera 6 (1983), a six-voice analog polysynth with dual DCOs, SSM 2044 filters, velocity sensitivity, and MIDI, later re-released as the DK600. Siel also produced the Mono monosynth, the DK70 and DK80 keyboards, and the DK700.

Siel was acquired by Roland in 1987, which absorbed its sales and distribution channels and used the operation as the basis for its Italian R&D presence. The brand's vintage instruments remain sought after on the used market for their warm analog character and distinctive Italian voicing.

Siel has 8 products cataloged on Equipboard, including Synthesizers. Their gear is featured by 13 artists, with the strongest followings in Electronic, Rock, and Pop. Notable users include Adrian Utley, Victoria Legrand, and A. G. Cook.