This paper reflects on the double status of observer and activist in the ethnographic study of the Socialist Party (PS). It stresses the benefits of research conducted from this vantage point but also highlights its limits and failings. The behaviors of the observed actors are always influenced by role assignment, which is clearly more fluid and contradictory in this case. This renegotiation over time takes a special form as the dual identity requires the restitution of the research outcomes to the actors.