The Burst Alert Telescope (BAT: 14-150 keV) on board of Swift is mainly devoted to the monitoring of a large fraction of the sky (50%-80% per day) for the occurrence of Gamma Ray Bursts. This provides the opportunity for a substantial gain of our knowledge of the Galactic and extragalactic sky in the hard X-ray domain. The Second Palermo Swift-BAT hard X-ray catalogue, obtained from the analysis of the data relative to the first 54 months of the Swift mission includes about 1300 BAT sources, 1100 of them associated to a softer counterpart using a large follow-up campain with Swift/XRT. I will present the general properties of the catalogue and some highlights on the analysis of individual sources.