Hydrogen is liquefied by a process comprising pre-cooling hydrogen feed gas by indirect heat exchange against pressurized liquefied natural gas (“LNG”) to produce pre-cooled hydrogen feed gas and pressurized natural gas, further cooling at least a portion of said pre-cooled hydrogen feed gas by indirect heat exchange against at least one refrigerant to produce condensable hydrogen gas and expanding at least a portion of said condensable hydrogen gas to produce at least partially condensed hydrogen. One advantage of such a process is that the power consumed during liquefaction is significantly less than that consumed in existing hydrogen liquefaction processes which pre-cool hydrogen feed gas by indirect heat exchange against other refrigerants, e.g. liquid nitrogen.