the baby boom generation, born between 1946 and 1964, is creating a shift in canada towards an aging population. in 2031, 22.8% of the population will be over the age of 65, compared to 14.1 in 2011 (statistics canada, 2010). although it is well known that physical activity is an integral aspect of healthy aging (swan, friis, & turner, 2008) and that the benefits of physical activity far outweigh the risks, less than 50% of baby boomers participated in regular physical activity in 2010 (statistics canada, 2011). theoretical research using the theory of planned behaviour (tpb) and the stages of change model (scm) has been used extensively in the behavioural health field. to our knowledge, no study has focused on the baby boom population specifically and their behaviour and intentions toward physical activity. method: one-hundred and seventy male and female baby boomers (aged 45 to 66) participated in the study. using questionnaires, stage of change (scm), demographics, attitudes, subjective norm, perceived behavioural control, behavioural beliefs, normative beliefs, control beliefs (theory of planned behaviour; tpb) and exercise behaviour (godin leisure time exercise questionnaire; glteq) were assessed. results: stepwise regression analyses indicated that the tpb constructs predicted 35.6% of physical activity intention, and intention predicted 29.4% of physical activity behaviour. statistical differences were seen between the scm contemplators and preparers and the action and maintainers on the tpb constructs. conclusions: the tpb produced important theoretical insight into the physical activity intentions and behaviours of baby boomers based on participants’ stage of change. pbc and attitudes were the strongest predictors of intention. these findings suggest that these constructs should be targeted in interventions designed to increase physical activity participation in the baby boom population.