ALPI is a superconducting linear accelerator under completion at the Laboratori Nazionali di Legnaro. The accelerating elements are quarter wave resonators with a thin film of lead as superconductor. They are cooled at 4.5 K by means of liquid helium provided by an on-line liquifier/refrigerator system. The main features of the cavities, cryostats, cryogenic plant and vacuum system are described.