There is a growing interest in using robots in dangerous environments, such as for exploration, search-and-rescue or monitoring applications, in order to reduce the risks for workers or rescuers and to improve their efficiency. Typically, flying robots offer the possibility to quickly explore large areas while ground robots can thoroughly search specific regions of interest. While existing robotic solutions are very promising, they are often limited to specific use cases or environments. This makes them impractical for most missions involving complex or unpredictable scenarios, such as search-and-rescue applications. This limitation comes from the fact that existing robots usually exploit only a single locomotion strategy, which limits their flexibility and adaptability to different environments. In this thesis, a multi-modal locomotion strategy is investigated as a way to increase the versatility of mobile robots. We explore integrated design approaches, where the same actuators and structure are used for different modes of locomotion, which allows a minimization of the weight and complexity of the robot. This strategy is challenging because a single locomotor system must accommodate the potentially conflicting dynamics of multiple modes of locomotion. Herein, we suggest taking inspiration from nature, in particular the common vampire bat \emph{Desmodus rotundus}. The goal being to make multiple modes of locomotion dynamically compatible (i.e. have compatible speeds and torques requirements), by optimizing the morphology of the locomotor system and even by adapting the morphology of the robot to a specific mode of locomotion. It is demonstrated in this thesis that the integrated design approach can be effectively implemented on a multi-modal aerial and terrestrial robot, and that two modes of locomotion can be made dynamically compatible by optimizing the morphology. Furthermore, an adaptive morphology is used to increase the efficiency of the different modes of locomotion. A locomotor system used both for walking on the ground and controlling flight, has been successfully implemented on a multi-modal robot, which further has deployable wings to increase its performances on the ground and in the air. By successfully exploiting the concepts of integrated design and adaptive morphology, this robot is capable of hovering, forward flight and ground locomotion. This robot demonstrates a very high versatility compared to state of the art of mobile robots, while having a low complexity.