In a single dosage-unit, capsule-in-capsule formats provide various release phases for a single or multidrug substance.The format also may deliver combinations of compounds that otherwise would be incompatible.The author outlines how to choose carriers and capsule shells according to dosage requirements and intended use.Example in vitro data demonstrate the flexibility of the capsule-in-capsule system.Finally, the author examines the approach's suitability for manufacturing and commercialization.