The investigators are working with three Pulmonary Rehabilitation (PR) teams in South Yorkshire (from Sheffield, Rotherham and Doncaster). PR is an education and exercise programme for people with lung conditions, which aims to teach people the skills to help them self-manage their condition. The first part of this feasibility study will investigate how PR is currently being delivered, and whether there would be any scope to include the app during and after PR to help people increase (or at least maintain) their physical activity levels longer term. This will be done by observing PR sessions, looking at how PR is delivered and referrals to the service, and through interactive workshops with healthcare professionals who deliver PR. The second part of the project will involve 'trying out' the app with a small group of people with COPD who are attending PR, to investigate whether the app is easy to use, whether any changes are needed, and the best way to use the app in the future. In order to determine whether the app successfully helps people with COPD to increase their physical activity levels, the investigators will need to carry out a much larger study in the future which compares use of the app with not having the app. The current feasibility project will help with planning this much larger study.