A reformatory or reformatory school is a youth detention center or an adult correctional facility popular during the late 19th and early 20th centuries in Western countries. In the United Kingdom and United States, they came out of social concerns about cities, poverty, immigration, and gender following industrialization, as well as from a shift in penology to reforming instead of punishing the criminal. They were traditionally single-sex institutions that relied on education, vocational training, and removal from the city. Although their use declined throughout the 20th century, their impact can be seen in practices like the United States' continued implementation of parole and the indeterminate sentence.