The story of the Lex Ecclesiae fundamentalis takes place in the context of the reform of the Canon Law Code, one of the essential point in the programme of the Second Vatican Council. Starting with the publication of the Textus emendatus in 1971, the document's development goes on until 1983, when, approved the new Codex, pope John Paul II decides to reject the scheme. Therefore, the following paper intends to reiterate the history of this document, analysing the main stages of its drafting history and the debate that, concurrently, animates the ecclesiastical and scientific enviroment in a church just came out from the 'epochal transition' of the conciliar experience.