In this thesis, an interactive document preparation system, "FITS (Full-screen Interactive Typesetting System)", that combines such seperate functions of "editor" and "formatter" into a single system is described. In the FITS, a local chance in a document can be interactively specified in a manner independent of an output device and its effect can be immediately seen on a full 2D screen by displaying only the page affected. The FITS consists of five parts: a EDITOR part, a PREPROCESSOR part, a FORMATTER part, a DISPLAY MANAGER part and a PAGE MAKEUP part. It has been programmed in FORTRAN and running on VAX-11/780 mini-computer system with VT-100 display at KAIST.