Microscale robots have been the focus of extensive research efforts resulting in various innovative developments that broaden their capabilities and applications. The rational design of materials has been the cornerstone for developing and innovating microscale robots, and breakthroughs in materials science are expected to further push the boundaries of this field. This Review provides an overview of the design principles and material selection for the propulsion and operation of microrobots. The fundamental mechanisms governing the motion of microrobots are first introduced, followed by the material design strategies enabling efficient and controllable propulsion. We highlight the use of diverse reactive and responsive materials in realizing the advanced functionalities and capabilities of microrobots, cover representative biomedical and environmental applications and discuss how future material innovations will impact the development of next-generation microscale robots.