The Biopharmaceutical Classification System (BCS) classifies drug compounds based on their solubility and permeability properties. The BCS can be used to predict in vivo pharmacokinetics and determine when a waiver for bioavailability and bioequivalence studies may be requested. BCS Class I drugs that are highly soluble and permeable are most suitable for oral administration as they are rapidly dissolved and absorbed. The BCS aids in drug development by using solubility and permeability measurements to predict in vivo drug performance and guide biowaiver considerations.