Measurements of magnetic fields and charged particles near Mars made over the past 4 decades teach us about its plasma environment, upper atmosphere, near-surface environment, subsurface, and deep interior. The upper atmosphere and plasma environment of Mars are of interest because they are the sites of energy exchange between the planet and its surroundings, dominated by the Sun and solar wind. It is difficult to understand the state and evolution of the Martian system without understanding this important upper boundary. A number of recent spacecraft observations demonstrate that the exchange of particles and energy between the solar wind and atmosphere is particularly dynamic at Mars. Dr. Brain will discuss two examples and their implications: the escape of atmospheric particles via bulk removal processes, and localized energy deposition characterized by ultraviolet aurora on the Martian night side.