This book investigates the geology, petrology, geochemistry and petrogenesis of some old granite plutons in Sinai as a typical example for the orogenic continental arc granitoids. It presents comprehensive view on their field and petrographic characteristics including; country rocks, nature of contacts, outcrop morphology, mineralogy, texture, structure and enclaves and xenolithes. All of these granitic plutons have an explicit calc-alkaline nature, and a prevalent metaluminous character. Their magmatic evolution was interpreted in terms of simple fractional crystallization accompanied by slight mixing processes. Melt temperatures attained during their formation were estimated between 740-924°C. They are distinguished as high-temperature tonalitic (Cordilleran) I-type granites that were derived by partial melting of infracrustal mafic M-type rocks of primitive island arcs, underplated beneath the crust in the deep crust or perhaps modified mantle. Paleotectonic environment investigations infer that they are continental arc granites intruded at active continental margin prior to plate collision by partial melting of infracrustal mafic rocks underplated beneath the continental crust