The third computer designed and built by Konrad Zuse and the first computer to successfully run real programs. The computer was ready in 1941, five years before ENIAC.

Zuse began his work on program-driven calculating machines in 1935. His two predessors of the Z3, the Z1 and Z2, were unsuccessful mechanical calculating machines. The Z3 was delivered to the Deutsche Versuchsanstalt für Luftfahrt (German Experimental Department of Aeronautics) in Berlin and was used for deciphering coded messages. In 1998, there may still be models of Z3 in museums .

The Z3 used about 2600 relays of the kind used in telecommunications. Zuse wrote and implemented the language Plankalkül on the Z3. Programs were punched into cinefilm.

Zuse built some more computers after World War II, including the Z3's successor, the Z4, which was set up at ETH Zurich, Switzerland.

Of the potential rival claimants to the title of first programmable computer, Babbage (UK, c1840) planned but was not able to build a decimal, programmable machine. Atanasoff's ABC, completed in 1942, and Eckert and Mauchly's ENIAC (US, 1945/46) were special purpose calculators, like those of Pascal (1640) and Leibniz (1670). None of these machines was freely programmable. Neither was Turing et al.'s Colossus (UK, 1943-45). Aiken's MARK I (1944) was programmable but still decimal, without separation of storage and control.