OBJECTIVE. We describe the development of a questionnaire, Participation in Activities and Places Outside Home (ACT-OUT). for older adults with cognitive impairment and align it to people with mild- to moderate-stage dementia. METHOD. ACT-OUT was developed in a cross-cultural collaboration in combination with three rounds of cognitive interviews in Switzerland with 26 older adults without cognitive impairment and five older adults with dementia. Qualitative data from the interviews were analyzed using a constant comparison approach. RESULTS. The final ACT-OUT Version 1.0 consists of three parts: (1) questions targeting places older adults visit: (2) questions on aspects influencing participation , such as transportation. familiarity, and risk perception: and (3) questions on perception of self. CONCLUSION. The development of an instrument such as ACT-OUT is more a cyclical than a linear process. This study is a first step toward a more systematic evaluation of out-of-home participation among older adults with and without dementia.