The Doepfer A-100 is an analog modular synthesizer system introduced by German audio manufacturer Doepfer in 1995. Although there were only 10 module types at time of release, it currently has more than 120 modules plus several different enclosures and accessories.

Modular synthesizers are synthesizers composed of separate modules for different functions. The modules can be connected together by the user to create a patch. The outputs from the modules may include audio signals, analog control voltages, or digital signals for logic or timing conditions. Typical modules are voltage-controlled oscillators, voltage-controlled filters, voltage-controlled amplifiers and envelope generators.