This paper describes how Prolog was used for the development of a new concurrent realtime symbolic programming language called Erlang. Erlang was developed by first building a prototype in Prolog - the prototype was used by a user group to test their reactions to the language. As time passed many features were added (and removed) from the interpreter and eventually the language reached a level of maturity where it was decided to try it out on a significant problem. About 3 years and some 20,000 lines of Erlang later, performance became an issue - we wrote Prolog cross compilers from Erlang to various concurrent logic programing languages followed by a direct implementation of Erlang itself. The direct implementation of Erlang was loosely based on the WAM and made by writing a Prolog compiler from Erlang to a new abstract machine and an emulator for the abstract machine in 'C'. The instruction set for the abstract machine was first prototyped in Prolog - finally the compiler was re-writ...