I enjoy searching for physical explanations for what we observe in the Universe. My interests range over the formation of galaxies and their large-scale distribution in space, the composition of the Universe, the intergalactic medium, the formation of massive black holes and the nuclear regions of galaxies, and gravitational lensing as a probe to the nature of dark matter. Over the last few years I have focused on the large-scale distribution of intergalactic gas probed by spectroscopic surveys of quasars observing hydrogen in absorption. This is revealing crucial clues on both the initial conditions of the Universe and the formation of galaxies. At present I am looking at techniques to inquire on the nature of the dark matter, among them the observation of extremely magnified high-redshift stars close to the critical curves of clusters of galaxies acting as gravitational lenses. I am also interested in theories of light axions or scalar fields as promising candidates for the dark matter.