Inertial sensors have the potential to transform the field of human gait stability by enabling experiments to be conducted outside conventional laboratory conditions. New topics can potentially be explored, including observation of how gait stability of walking individuals is influenced by robots. This thesis aims to validate the use of an inertial sensor motion capture system for measuring gait stability of walking humans, and then to apply that system to examine how an accompanying robot affects human gait. First, we tracked walking participant motion using optical and inertial sensors and calculated stability measures. Analysis revealed that inertial sensors could be used to find similar differences between walking behaviours as the optical motion capture system, despite error in the values of the measures. Next, we used inertial sensors to evaluate gait stability as participants walked alone and with a small quadruped robot, finding that participants walked more slowly and with altered stability when walking with the robot. As part of the same experiment, we used optical motion capture to observe some trends between robot behaviour and human gait, which demonstrated that adaptations were related to the robot’s movement.