Disclosed are containers (100) for cryopreserved biological samples (102), which comprise an insulated housing comprising a cavity (108) for containing at least one cryopreserved biological sample； and a sealed reservoir (106) at least partly surrounding the cavity, the sealed reservoir comprising liquified gas (120) such as liqified air, the gas being kept largely liquified by means of a heat transfer engine (112) such as a Stirling cryocooler. A valve (114) may be provided to function as both a pressure relief valve and an inlet valve. The inlet valve may be coupled to a sensor (122) for sensing a volume of liquified gas within the sealed reservoir. The container may further comprise a heat exchanger (116) coupled to the heat engine and extending into the sealed reservoir.
