Microspheres are one of the multiparticulate delivery systems and are prepared to obtain prolonged or controlled drug delivery to improve bioavailability/stability of the poorly soluble drug and to target the drug to specific sites. Moreover the cross-linked microsphere have tremendous potential in the area of controlled release dosage form design and also solve the problems associated with the delivery of poorly soluble drugs. This book provides preparation of atorvastatin calcium loaded ethyl cellulose microsphere using different kinds of crosslinking agent (Glutaraldehyde, Formaldehyde, tween 20), in-vitro characterization including Fourier transform infrared spectroscopy, Differential Scanning Calorimetry, Particle Size Analysis, Scanning electron microscopy, Drug content, Entrapment efficiency, In vitro Release Study and Micromeretic properties, which may create the interest to students, teachers and researchers to develop their knowledge in chemical cross linked microspherepreparation and their controlled / prolonged drug release manners.