The astonishing progress in computer software and hardware technology in recent decades has established Computational Chemistry as a legitimate and exciting means of learning and exploring chemistry. Computational Chemistry has become a powerful tool for elucidating elusive mechanistic details of chemical reactions. An understanding of the detailed mechanistic pathways of organometallic reactions will drastically increase the ability to design and ?fine tune'' catalytic activities and selectivities and, thereby, sustain the importance, distinctiveness and vitality of the field. Density functional theory studies of the mechanistic pathways for the oxidation of ethylene by chromyl chloride, the olefin metathesis reaction and the transition-metal-assisted formation of 1,2-dinitroso complexes are reported. This book should be a very useful reference for all those who are interested in how computational chemistry can be used to unveil intricate details concerning the course of chemical reactions and provide insight otherwise unavailable into reaction mechanisms.