After a decade of intense negotiations and overcome innumerable obstacles the final step has been taken in order to the Treaty of Lisbon to enter into force in December 1,2009. The last of such obstacles, but not the least, concluded when the Czech Republic deposited the ratification instruments corresponding to that country, in Rome, depository seat of the institutional documents of the Union. This text analyzes the diferent stages that the European jurists had been profiling until define the role that the religious factor has in the legal system.