AbstractObjectivesPhysical activity is an important health behaviour especially for older adults. Forming implementation intentions is an effective strategy to implement physical activity in daily life for young and middle‐aged adults. However, evidence for older adults is inconclusive. This study explored the thoughts of older adults about implementation intentions and potential barriers and facilitators while formulating them.MethodsThree samples of older adults from the United Kingdom (n = 8), Germany (n = 9) and Switzerland (n = 17) were prompted to think aloud while formulating implementation intentions to be more physically active. After the task, semi‐structured interviews were conducted. Data were analysed thematically.ResultsParticipants expressed pre‐established thoughts about implementation intentions (e.g. they feel too restrictive). During the formulation of implementation intentions, several barriers to creating them were reported (e.g. problems with finding cues due to absence of recurring daily routines), but participants also mentioned that forming implementation intentions acted as a facilitator for physical activity (e.g. cues as useful reminders to be active, task itself triggering self‐reflection about physical activity). After the task, participants reflected on circumstances that decrease the likelihood of enacting implementation intentions (e.g. spontaneous alternative activities, weather, health‐related barriers, Covid‐19‐related barriers), which triggered spontaneous coping planning.ConclusionsThe results on barriers and facilitators of implementation intentions and physical activity from older adults' perspectives provide starting points for improving instructions for older adults on how to create implementation intentions for physical activity. Future studies are needed to investigate whether the findings extend to implementation intentions for other behaviours.