For generations social thinkers have disagreed upon why some people get involved in prostitution. Some researchers emphasize structural factors such as poverty,social marginalization or family problems, while others describe participation in prostitution as a voluntary choice. As a consequence contemporary research on prostitution tends to focus on prostitutes as either victims of a general social problem or as a manifestation of (female) agency. Unlike previous research based on self-reported questionnaires and/or interviews, this study integrates social security numbers of people in prostitution with national register data. Internationally this is unique and provides the opportunity to examine the social background of men and women in prostitution with an unseen level of detail. In addition the study includes lifestory interviews with active prostitutes to gain knowledge on what they consider to be of importance, when explaining their involvement in prostitution.