Introduction: Sedentary behaviour (SB) has a deleterious effect on health and physical function in older adults (OA). Yet, there is little known about how to change SB patterns in OA. This thesis aimed to: 1) define the extent and context of SB in older adults; 2) develop an intervention to help reduce SB in OA using known physical activity behaviour change motivational techniques; 3) pilot this intervention, using activity monitoring and real time or follow-up feedback, to motivate frailer OA to reduce their SB. Methods: 1) Systematic Review: Eighteen studies (23 papers) were included to define prevalence of SB and 22 studies (31 papers) were included to define amount of SB in OA; 2) Mixed Methods: Exploration of context of SB, to develop the intervention, was undertaken in two lifelogging studies. Six OA reported in-depth description of context alongside camera images and objective SB monitoring; Thirty six OA used a standard classification system to report context; 3) Pilot Randomised Controlled Trial (RCT): The Stomp Out (prolonged) Sitting (SOS) Intervention recruited OA living in sheltered housing complexes (N=23) and consisted offace-toface discussions, including visual feedback, about their SB on weeks 2, 6 and 10. They were monitored continuously over 14 weeks with an activPAL. One group had the addition of real-time feedback, via a vibrational feedback function (VTaP). The primary outcomes were SB parameters and secondary outcomes were physical function and self-reported wellness, analyzed with mixed model analysis. The participants also reported effects of the intervention and behaviour changes made via a self-report questionnaire, analyzed thematically.