This textbook provides information on using and implementing FORTH and is aimed at readers with some experience of programming in another language such as Basic. FORTH-83, the new implementation, is used throughout the book. The differences between this and the widely-used FORTH-79 are discussed, and in addition the author refers to MMSFORTH and the multi-user version POLYFORTH. The reader is lead carefully through the complexities of the language, enabling a deep understanding of the fundamental programming structure. A number of exercises have been included in the text, and model answers to these are provided.