The Guido Engine Library is a generic, portable library and API for the graphical rendering of musical scores. The library is based on the GUIDO Music Notation Format as the underlying data format. It takes account of the conventional music notation system and should be flexible enough to include any graphical sign and musical information if necessary. The GUIDO Music Notation Format [GMN] is a formal language for score level music representation. It is a plain-text, i.e. readable and platform independent format capable of representing all information contained in conventional musical scores. The basic GUIDO Format is very flexible and can be easily extended and adapted to capture a wide variety of musical features beyond conventional musical notation (CMN). The GUIDO design is strongly influenced by the objective to facilitate an adequate representation of musical material, from tiny motives up to complex symphonic scores. GUIDO is a general purpose musical notation format; the intended range of application includes notation software, compositional and analytical systems and tools, performance systems, and large musical databases. It is powerful, flexible, easily portable, and human readable.