Organic molecules are the proficient materials which have been used in Organic field effect transistors and organic thin film transistors. Oligocenes studied for several decades currently provides among the best semiconductors in the field of organic electronics. The interest in the class of oligothiophene materials has also been intense ever since the first organic transistor. Metal phthalocyanines (MPcs) are planar or nearly planar organic molecules with a metal ion or a metal compound ion in the center. These molecules show interesting optical and electronic properties such as high photoconductivity and electroluminescence. This book deals with three major classes and presents the electronic, photophysical and charge transfer properties. Moreover, we also focused how to simulate the crystal structures. The last chapter deals with the packing effect on the intrinsic mobility. How stability can be improved has been discussed. Finally, this book deals with the major issues (a) simulation/prediction of the crystal structures (b) How to enhance the intrinsic mobility © How to improve the stability.