18 U.S.C. § 4081: Classification and treatment of prisoners

The Federal penal and correctional institutions shall be so planned and limited in size as to facilitate the development of an integrated system which will assure the proper classification and segregation of Federal prisoners according to the nature of the offenses committed, the character and mental condition of the prisoners, and such other factors as should be considered in providing an individualized system of discipline, care, and treatment of the persons committed to such institutions.