United States federal probation and supervised release are imposed at sentencing. The difference between probation and supervised release is that the former is imposed as a substitute for imprisonment, or in addition to home detention, while the latter is imposed in addition to imprisonment. Probation and supervised release are both administered by the U.S. Probation and Pretrial Services System. Federal probation has existed since 1909, while supervised release has only existed since 1987, when it replaced federal parole as a means for imposing supervision following release from prison.