This thesis discusses our design of the Passive Magnetic Heat Switch (PMHS). This project, funded by NASA, looks for new, low TRL heat switches for Lunar Rover applications. The novelty of the PMHS is its ability to switch near room temperature by using temperature dependent magnets. The PMHS is a gap closure heat switch where the ON state mates highly polished copper surfaces and the OFF state de-mates the surfaces. We use commercial neodymium magnets to close the gap in the ON state and gadolinium, which has a Curie temperature of 20 °C, to achieve the OFF state. All experiments were performed under high vacuum and reasonably agree with our FEA models. The PMHS turns ON at 28.5 °C and turns OFF at 15.5 °C. The ON and OFF state conductances, are 0.153 WK-1 and 0.0099 WK-1 respectively. The switch ratio, which is the figure of merit for all heat switches, is 15.5:1.