The overall objective of this thesis was to compare compensatory reactions in young and older adults following unexpected platform perturbations in the frontal and sagittal planes during gait. Eleven young (aged 18-30) and ten community-dwelling older adults (aged 65+) completed a general health questionnaire, Mini BESTest, hip strength tests, and 45 walking trials on a motion platform. The walking trials were completed in a randomized block design on a 5 m pathway that moved following right heel contact after at least two steps. Young adults had stronger hips and performed better on the Mini BESTest than older adults. Compensatory reactions (measured through gait parameters and centre of mass motion) indicated that lateral perturbations were more difficult for both groups. These measures showed that young adults were able to recover more quickly than older adults. This could be attributed to altered base of support changes that occurred immediately following platform motions. / Ontario Graduate Scholarship