Stirling cycle machines, including engines and coolers or heat pumps are described. In a disclosed arrangement, there is provided a Stirling cycle engine, comprising: an expansion volume structure defining an expansion volume; a compression volume structure defining a compression volume; a gas spring coupling volume structure defining a gas spring coupling volume; a first reciprocating assembly comprising an expansion piston configured to reciprocate within the expansion volume and an expander gas spring piston rigidly connected to the expansion piston and configured to reciprocate within the gas spring coupling volume; and a second reciprocating assembly comprising a compression piston configured to reciprocate within the compression volume and a compressor gas spring piston rigidly connected to the compression piston and configured to reciprocate within the gas spring coupling volume, wherein the gas spring coupling volume structure and the first and second reciprocating assemblies are configured such that power is transferred in use from the expansion piston to the compression piston via the gas spring coupling volume.