A reciprocating cryogenic pump (2) comprises a piston reciprocable within a pumping chamber (44). The pumping chamber (44) has an inlet suction valve (48) for cryogenic liquid to be pumped and an outlet (32) for high pressure cryogenic liquid. The inlet valve (48) for the cryogenic liquid communicates with a cryogenic liquid reception chamber (46) in the cold end or head (6) of the pump (2). The pump head (6) is at least partially surrounded by a first jacket (8) retaining primary vacuum insulation. The first jacket (8) is itself at least partly surrounded by a second jacket (10). The jacket (10) defines a chamber for the reception of a coolant fluid such as liquid nitrogen and the second jacket has an inlet (20) and an outlet (22) for the liquid nitrogen. The thermal insulation can be further enhanced by a trapped gas space (73) between the first jacket (8) and an inner sleeve (52), the latter defining with an outer sleeve (50) vacuum insulation for the pumping chamber (44).