The Conference entitled The Foundations of Quantum Mechanics. Historical Analysis and Open Questions - Cesena 2004 was held in Cesena (Italy) from October 4 to October 9, 2004, and was the fourth of a series that began with a Conference in Camerino (October 31-November 3, 1988) and continued with two Conferences in Lecce (October 5-8,1993, and October 13-16, 1998). All Conferences had the same title, in order to underline their ideal continuity. Indeed, they all were conceived as interdisciplinary meetings among Italian researchers (physicists, logicians, mathematicians, historians and epistemologists) concerned with the history, the structures and the foundational problems of quantum mechanics (QM).