Bioequivalence is a vital concern in drug development even more significant in the case of Narrow Thera-peutic Index (NTI) drugs. In clinical development of New Chemical Entities (NCE), bioequivalence studies necessitate to be performed when the formulation of the pharmaceutical dosage form has been changed. In vivo pharmacokinetic data can be used as surrogate parameters for in vivo solubility and permeability data. The Biopharmaceutics Classification System (BCS) has emerged as a helpful tool in product development by alluding to the in vivo performance of the active substance. The bio-relevance of the BCS properties and the in vitro release are best expressed through a correlation between in vitro and in vivo data. Recently BCS has been implemented for waiving bioequivalence studies on the basis of the solubility and gastrointestinal permeability of drug substance and can be strategically deployed to save time and resources during generic drug development. The BCS has been adopted as a very useful tool for in vivo drug design and development worldwide, particularly in terms of regulatory standards. A BCS-based biowaiver has become an important and cost-saving tool in approval of generic drugs.