Electrohydrostatic actuators (EHAs) are known for their high power efficiency, reliability, compactness, and easy maintainability. However, uncertainties can cause their performance to degrade or even lead to accidents, especially faults such as actuator internal leakage. Therefore, there is a need to design robust controllers capable of dealing with these uncertainties. To design a controller, a mathematical model is usually derived first. One method of deriving a model is the use of physical laws, which is easy to implement. However, this can result in conservative designs, because of the imprecise model and parameter ranges. Another solution is to implement system identification techniques. While this can avoid conservatism, it may have difficulty in identifying a system in some cases. Apart from double-rod EHAs, single-rod EHAs also have a wide range of potential applications. Given the asymmetry in the piston effective areas, a circuit with four possible configurations must be designed to compensate for asymmetrical flows. However, during configuration changes, the behavior of most existing circuits may not be satisfactory, which might not guarantee the desired control performance and necessitates designing robust controllers capable of operating in all circuit configurations. In this thesis, robust controllers based on quantitative feedback theory (QFT) are designed for EHAs. First, a QFT controller with tolerance to internal leakage is designed for a double-rod EHA positioning system. The controller is further augmented with a friction compensator, and its efficacy is examined in both simulations and experiments. Then, a mathematical model is derived using system identification (instead of physical laws) to develop a low-bandwidth position controller. Experimental results show that the designed controller has low bandwidth and can satisfy the specifications. Moreover, a QFT position controller and a QFT velocity controller are also designed for a newly developed single-rod EHA that operates in all circuit configurations, and their effectiveness are demonstrated in the experimental results.