Concerns about the environmental impact of refrigerants used in vapour-compression heatpumps and refrigerators, have prompted the Stirling-Cycle Research Group at the University of Canterbury to investigate the feasibility of low-cost Stirling-cycle machines that use air as the refrigerant. Such machines theoretically have the highest efficiency possible for any practical thermodynamic system, and thus provide a tempting alternative to traditional vapourcompression technology. This paper outlines the working principles of Stirling-cycle heat-pumps and refrigerators, and describes some of the work performed at Canterbury University. Some of the heat-pump development programme results are also presented, and briefly discussed.