Glycogen Synthase Kinase is a very large family of metabolically and physiologically important bio catalysts. Specifically, GSK 3 are of prime importance in case of its role in treatment of various diseases as well as other biological reactions. GSK3 is unusual in that its protein kinase activity is high in resting cells. Cellular stimulation through plethora of signaling pathways typically results in rapid and reversible reduction in its catalytic activity. Genetic analysis and use of selective inhibitors have shown that GSK3 plays a critical role in development, metabolic homeostasis, neuronal growth and differentiation, cell polarity and cell fate as well as modulation of apoptotic potential. This book will be helpful to students and researcher working in biochemistry specifically enzyme technology to get deeper insight of the role of enzyme.