The general objective of this thesis was to examine the postural responses of young and older adults during reactive and self-paced voluntary postural sway tasks. To achieve this objective, three specific aims were addressed: (1) to determine if differences exist in the reaction time of voluntary postural sway movements between young adults, and low and high falls-risk older adults, (2) to determine if differences exist in coordination during the performance of voluntary postural sway movements between young adults, and low and high falls-risk older adults, and (3) to determine the combination of voluntary postural sway tasks, sway directions, and balance measures that best predict the falls-risk and falls-history status of community-dwelling older adults. The falls-risk and falls-histories of the older adults were determined based on an assessment of sensorimotor and balance function by the Physiological Profile Assessment (PPA), and self-reported 12 months history of falls, respectively. Four experiments were conducted to examine the performance of voluntary postural sway movements in the anterior-posterior (AP) and medial-lateral (ML) directions. The specific voluntary postural sway tasks were maximum static leans, maximum voluntary postural sway, continuous voluntary postural sway, rapid initiation of voluntary postural sway, rapid termination of voluntary postural sway, and rapid orthogonal switches of voluntary postural sway between the AP and ML directions. Measures of task performance included reaction time, the amplitudes of the centre of pressure (COP) and centre of mass (COM) in the AP and ML directions, the level of coupling between motions of the COP, trunk, and head, and the separation distance between the COP and COM (COP-COM) in the AP and ML directions. The age, falls-risk, and falls-history groups were compared for differences in these measures, and the predictive capacity of these measures for group status were evaluated.