Magnetocaloric heat pumps (MHPs) use the solid-state magnetocaloric effect (MCE) to move heat from cold to hot using an intermediate heat-transfer fluid. Work input is required to drive the MCE via a change in a magnetic field. Work input is also required to drive the heat-transfer fluid flow. Thus design of a MHP involves the coupling of materials, magnetics, heat transfer, and fluid flow. We discuss design principles and operational devices that have brought this technology toward technical feasibility, and the approaches to overcome remaining hurdles to commercial feasibility.