An individual’s tendency to adjust their behaviour, to unconsciously copy the gestures of another, is known as nonconscious behavioural mimicry. Chapter One reviews the facilitative role mimicry plays in social interactions and the underlying mechanisms of behaviour matching effects. However, the conditions under which mimicry occurs are not well characterised and, although accepted to be an automatic effect, this assumption remains empirically untested. This thesis examined the methods used to elicit mimicry and further explored the mechanisms underlying the effect. Chapter Two developed a paradigm to demonstrate mimicry relative to a suitable control condition and examined the generalisability of the effect to alternative gestures. However, mimicry was not observed. It was suggested that the target gestures were presented too overtly, and participant’s awareness was responsible for not demonstrating mimicry. Toward the refinement of the paradigm, Chapter Three focused on aspects of gesture presentation, namely, duration of exposure and gesture type. Although Experiment 2 found that mimicry was not influenced by the duration of exposure to target gestures, Experiment 3 showed that mimicry can generalise to alternative, localised, gestures. Crucially, both experiments demonstrated mimicry compared to an equivalent control condition. Chapters Four and Five examined the automaticity of mimicry, specifically the efficiency and awareness criteria. Experiments 4 and 5 did not allow for clear conclusions to be drawn about the efficiency of mimicry. However, the results from Experiment 6 provided clear evidence that lack of awareness is necessary for mimicry to occur and, when mimicry did occur, participants were unaware of their own mimicry behaviour. It was concluded that mimicry meets one of the hallmarks of automaticity; operating without awareness. The results of these experiments are discussed regarding the reliability of the mimicry effect and the methodological and theoretical implications of these findings for the mimicry literature.