Development of a meaningful dissolution procedure and specifications for in-vitro and in-vivo applications (IVIVC) and assurance of product quality and batch-to-batch reproducibility in release profiles especially for modified release systems has been a challenge to both the pharmaceutical industries and the regulatory agencies. Both GI physiology and the physicochemical properties of the drug and behavior of the delivery system are important to the oral absorption. Dissolution study is particularly important for drugs that demonstrate absorption-rate limited or dissolution rate limited characteristics as defined by the Biopharmaceutics Classification System, BCS. In this respect a meaningful and discriminatory power of dissolution rate testing becomes critical and development of a sensitive, reliable in-vitro dissolution procedure for the quality of a product and prediction of its bioavailability is of primary goal and will be discussed in details.