  In this paper we review Castagnino's contributions to the foundations of
quantum mechanics. First, we recall his work on quantum decoherence in closed
systems, and the proposal of a general framework for decoherence from which the
phenomenon acquires a conceptually clear meaning. Then, we introduce his
contribution to the hard field of the interpretation of quantum mechanics: the
modal-Hamiltonian interpretation solves many of the interpretive problems of
the theory, and manifests its physical relevance in its application to many
traditional models of the practice of physics. In the third part of this work
we describe the ontological picture of the quantum world that emerges from the
modal-Hamiltonian interpretation, stressing the philosophical step toward a
deep understanding of the reference of the theory.
