Drug dissolution is a prerequisite to drug absorption and in vivo effectiveness for almost all drugs given in oral solid dosage forms. Drug absorption depends on the dissolution and solubilization of the drug under physiological conditions, and the permeability across the gastrointestinal tract. Because of the critical nature of the first steps, in vitro dissolution may be relevant to the prediction of biological response. Dissolution tests are applied to choose between formulation factors, assess the lot-to-lot quality of a drug product according to the biobatch; and ensure continuing product quality and performance after certain changes (e.g. in the formulation and manufacturing process, site of manufacture, scale-up). The recently developed Biopharmaceutical Classification System (BCS) has several benefits for recognizing how dissolution tests can be designed and which physiological factors have to be taken into consideration for the in vitro evaluation of solid dosage forms. Choice of test conditions (composition, volume and hydrodynamics of dissolution medium) should be based on where the drug is best absorbed in the gastrointestinal tract, and on whether it is administered in fasted or fed state. Duration of test and physiologically representative media can be selected to simulate gastric and intestinal environments according to the permeability profile of the drug, but mimicking in vivo hydrodynamics remains problematic and further research is required. To provide a basis for predicting the likelihood of achieving a successful in vivo-in vitro correlation, this review summarizes the biopharmaceutical considerations of in vivo drug release in accordance with the BCS.