18 U.S.C. § 3584: Multiple sentences of imprisonment

If multiple terms of imprisonment are imposed on a defendant at the same time, or if a term of imprisonment is imposed on a defendant who is already subject to an undischarged term of imprisonment, the terms may run concurrently or consecutively, except that the terms may not run consecutively for an attempt and for another offense that was the sole objective of the attempt. Multiple terms of imprisonment imposed at the same time run concurrently unless the court orders or the statute mandates that the terms are to run consecutively. Multiple terms of imprisonment imposed at different times run consecutively unless the court orders that the terms are to run concurrently. The court, in determining whether the terms imposed are to be ordered to run concurrently or consecutively, shall consider, as to each offense for which a term of imprisonment is being imposed, the factors set forth in section 3553(a). Multiple terms of imprisonment ordered to run consecutively or concurrently shall be treated for administrative purposes as a single, aggregate term of imprisonment.