This paper describes the Full-Hypermedia Educational Systems Development Model (FHESDM) for designing hypermedia systems that takes advantage (in terms of cognition and learning) of non-linear navigable structures and multimedia. The model is based on constructivist principles, including the subjectivity of the learning process, and assimilation and accommodation (i.e., blind exploration will involve a problematic situation for the student and solving it will advance the knowledge creating process), as well as some aspects of Ausubel's Significant Learning Theory. The model includes the contract concept that allows superimposing several navigation structures on an information structure to support a more customizable way of navigating through the system without taking the control from the student. (Contains 11 references.) (MES)