This is the first book to consider the difference women MPs make for women constituents in Britain by comparing women parliamentarians’ activities, priorities and perceptions to those of their male colleagues. It uncovers complicated gender dynamics that have been neglected in other works because of an exclusive focus on the activities of women MPs, and mounts a systematic challenge to the idea that a critical mass of women is necessary for women’s presence to matter. By comparing the representation received by women from a parliament with few women to that received from a parliament with many women, Anna Dionne leads the reader to understand why numbers are not magic. Her empirical research includes interviews with over eighty parliamentarians in London, Scotland, Wales and Northern Ireland, and the amassing of an unprecedented and comprehensive database of representatives’ legislative activities. She compares how men and women and different political parties introduce and support bills and motions, ask parliamentary questions, participate in committee and floor debates, and work behind the scenes for cross-party consensus and on constituency casework. The analysis considers gender similarities and differences throughout the policy process and explains the gender dynamics with a new sensitivity to their fluctuation.