This is a protocol for a Cochrane Review (Qualitative). The objectives are as follows:. Main objective: To identify the factors that create barriers or facilitate physical activity for people with a diagnosis of anxiety or depression from the perspectives of service users, carers, service providers and practitioners to help inform the design and implementation of interventions that promote physical activity. The overall aim of this review is to identify, appraise, and synthesise qualitative research evidence on the barriers and facilitators to engaging in physical activity in general lifestyle settings or as part of an intervention designed to increase physical activity for people with anxiety and depression. This will allow us to identify factors that create barriers and facilitators of physical activity in this population to inform the development, design, and implementation of future interventions. We will also integrate the findings from the QES with the two associated effectiveness reviews (Cooney 2014; Larun 2006). We will communicate our findings to public health commissioners and other stakeholders.