The most inactive people in our community stand to benefit the most from increasing their physical activity levels, but they may require support to do this. Peer-led physical activity programmes could be an important way to help increase older adults’ physical activity levels – by providing support to increase physical activity - but this needs to be tested. The Walk with Me study is testing the effectiveness of a peer-led physical activity intervention (the Walk with Me programme), that is delivered in the community by trained peer mentors.