In vitro-invivo correlation plays a key role in pharmaceutical development of dosage form, optimization of formulation. This articles describes about the regulatory criteria and the factors associated with developing an In-vitro and in-vivo correlation. This factors plays an important role in optimizing the design and protocol required fort development of any dosage form and to identify the bioavailability pattern of the dosage forms. This article provide information on the various guidelines, factors in developing the correlations, bio pharmaceutical classification system,and other applications.