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.[1] 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.[2][3] They were traditionally single-sex institutions that relied on education, vocational training, and removal from the city.[3] 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.[1]