Throughout the long-running BBC series Doctor Who, the Doctor has rarely been alone-his companions are essential. Male or female, human or alien, young or old, the dozens of companions who have travelled with him over the past 50 years have served as sympathetic proxies for the audience.

Through their adventures the companions are perfected, facing danger and thus discovering their strengths and weaknesses. Yet they all pay a price, losing their innocence and sometimes their lives. This collection of new essays examines the role of the companion as an intermediate between viewers and the Doctor. The contributors discuss who travels with the Doctor and why, how they interact, how the companions influence the narrative and how their journeys change them.