Spectroscopic datasets from orbiters and landers have been used to identify a growing variety of compositions on Mars. Evidence for sedimentary silica, sulfates, carbonates, phyllosilcates, iron oxides, and chlorides indicates a relatively rich and varied Martian aqueous history that is fundamentally changing our understanding of the planet. This increasingly detailed compositional picture can be used to infer the spatial and temporal extent of habitable environments as well as the potential for biological development and its subsequent preservation.