The ARP 2500 is a monophonic (or duophonic) analog modular synthesizer. It was the first product of ARP Instruments, built from 1970 to 1981. Although only about 100 units were made, Sound on Sound magazine later called it "undoubtedly one of the most important electronic musical instruments ever made." It is notable for being programmed via matrix switches instead of conventional patch cables. Demand for smaller and more affordable instruments led ARP to develop the semi-modular ARP 2600 and the fixed-architecture ARP Odyssey.

Initially made by Alan Pearlman’s company Tonus as the Series 2000 system, the company subsequently changed its name to ARP, after Pearlman's initials, and renamed the Series 2000 to the ARP 2500.

Designed by Alan Pearlman, Dennis Colin, and David Friend, the 2500 was advertised as having two major advantages over other synths: voltage-controlled oscillators with stable tuning and matrix switches instead of patch cords. The oscillators combined Alan Pearlman’s patented exponential converters with a dual core design, resulting in good tuning stability compared to competitors.

The sliding matrix switches found above and below the modules and are the main method of connection between modules and from the keyboards to the modules. There are rows of 1/8" jacks at the end of each row of matrix switches to interconnect rows of switches with wing cabinets or to serve as inputs and outputs. Keyboard connections are connected by default to the top left mini-jacks. Other major new features introduced in the 2500 were duophonic keyboards and a state variable filter. The main 2500 cabinet can hold 15 modules, and optional wing cabinets can each hold eight. The matrix switch interconnection scheme allow any module's output to connect to any other module's input. Unlike the patch cords found on the modular synths of competitors like Moog and Buchla, the matrix implementation enabled a cable-free experience. However, the matrix switches developed a reputation for dirty connections and crosstalk.

The earliest 2000 series cabinets could hold eight, fifteen, or nineteen modules. The later cabinets were taller, and available in 8 or 15 modules sizes. There was also a portable 8 module version, which they marketed as an expansion of the later 2600.

A range of five-octave keyboard options were available, including monophonic, split, duophonic, and dual versions. Split keyboards have one or two left octaves with reverse-colored keys, and either section could be monophonic or duophonic, offering control of up to four voices on a single keyboard.

Although the 2500 proved reliable and user-friendly, it was not commercially successful. Systems could cost up to $20,000, almost half the average US house price at that time, and the 2500 was introduced at a time when sales of large modular synthesizers were starting to fall, so they only sold approximately 100 units. ARP initially produced fourteen different modules, with many more planned to follow, but few of these prototypes made it into production.

Three additional modules existed only as prototypes or mock-ups: the 1012 Convenience module, the 1035 Triple modulator, and the 1040 Noiselator.