In this thesis our research goal is to develop, study and demonstrate multifunctional multi-robot systems in mesoscale. Particularly, our goal is to study and demonstrate terrestrial multi-locomotion and collective behaviours with mesoscale robots, similar to small-scale natural systems, by feeling the gap in the field. Our research objective is to develop, evaluate and demonstrate minimal, compact, variable power and efficient actuation mechanisms for multi-locomotion and rapid fabrication methods for robot multiplicity employing functional materials and composite design. In doing so, we intend to establish a comprehensive and systematic design methodology for designing multifunctional, mass-producible mesoscale robots for various applications. This dissertation first attempts to explore and answer the following key research question: how to achieve variable power, efficient and compact actuation in mesoscale? The relation between performance and physicality is significant for especially mesoscale robot design and is poorly studied. Our goal is to achieve high power, variable speed and high efficiency actuation in mesoscale. We attempt to address this by exploring unconventional active material-based actuation methods using shape memory alloy and composite material. In doing so, we quest of the following: what are the compromises should be made between force, speed, efficiency and size of functional material-based actuators? We investigate and demonstrate new, compact multimaterial actuators and mechanisms that possess power density superior to conventional motors, produce high speed and high force actuation and achieve multifunctionality when distributed and actuated selectively, all with minimal and compact forms and integrity. While we study and develop design methods at the component level, like actuation, based on performance and physical features, we look for the same at the composite level or robotic system level. The next research question we attempt to address is what, if any, is the general design methodology for constructing composite robots?. To address this we formulate and analyze robogami design in terms of mechanisms, geometry, functional components, materials and fabrication to highlight their relation, potential and the challenges, as well as to structure the knowledge in the field. This leads to a systematic design approach that consolidates these critical design features and facilitates robot design and fabrication process. To ensure applicability of our methodology, we analyze the design process of composite robots reported in the literature and design a multi-locomotion mesoscale robot, called Tribot, as a case study. We further investigate the application of the proposed actuation and rapid composite robot design methods by questing of how to achieve multifunctional multi-robot behaviors in mesoscale? We address this by constructing a unique, untethered, multi-locomotion robotic collective to study locomotion and cooperative behaviors. We investigate minimal, compact and tunable mechanisms that generate high power jumping and low power crawling locomotion. We overcome the key trade-off between the actuation power and weight and construct a 10 g palm-sized prototype, the smallest and lightest self-contained, multi-locomotion robot to date, by folding a quasi-2-D mechamatronic composite with locomotion mechanisms, smart actuation and sensing layers, enabling robot multiplicity assembly-free mass-production.