The aim of this thesis was to investigate whether observation of actions by others can affect the trajectory of a reach to an object, that is, the means by which that goal is achieved. This work has been inspired by the discovery of mirror neurons in primates and evidence that humans also possess a miITor system. The 13 experiments presented in this thesis used a reaching and lifting task involving obstacle avoidance to naturalistically manipulate the heights of reach trajectories. The results from these experiments provide strong evidence that people do simulate the specific kinematics of observed reaches, and that this affects the subsequent reach of the observer. Importantly, this demonstrates that the human miITor system is concerned with more than just behavioural goals, setting us apart from other primates. The effect was independent of viewing perspective, occurring both when participants sat next to and opposite each other. Action priming by observation did not occur in all circumstances. When participants viewed obstacle avoidance outside of peripersonal space priming did not occur. The final experimental chapter presents experiments that explored further the nature of the effect of peripersonal space, providing intriguing contrasts. In some circumstances the judgment of peripersonal space appears to be purely metric, rather than space that can be reached or acted within. The last pair of experiments, however, suggest that action priming may be affected by more than just the visual properties of the observed reaches, and that higher-level concepts, such as ownership, may effect priming.