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.