Gallium is a metal that literally melts in your hand. It has low toxicity, near-zero vapor pressure, and a viscosity similar to water. Despite possessing a surface tension larger than any other liquid (near room temperature), gallium can form nonspherical shapes due to the thin, solid native oxide skin that forms rapidly in oxygen. These properties enable new ways to pattern metals to create stretchable and soft devices with an unmatched combination of mechanical and electrical properties. This review summarizes the truly unique and exciting properties of gallium liquid metals.