he thesis entitled "Theoretical Studies of pie-Facial Selectivity in Organic Reactions" involve a computational examination of a suitable reactivity problem in organic chemistry. Systematic and efficient -procedures have been developed and tested for rationalizing observed face selectivities in numerous substrates. In a number of cases precise transition state structures have also been computed in a rigorous manner. The molecules examined are by and large sterically unbiased. Considerable emphasis has been placed on obtaining general interpretations, In particular, the relative contributions of various sterio electronic and electrostatic effect have been considered in detail.Predictions of a-face selectivities haw also been made in a few cases. In recent years many mildly perturbed substrates have been shown to undergo pie-face selective reactions. Chapter 1 provides a brief review of the available experimental result involving nucleophilic, electrophilic, radical and Diels- Alder reactions.The current status of theoretical understanding of theae rasults is also summarized.The discussion includes qualitative proposal as well as quantitative calculations on selected substrates. The principal goals of the present work and general features of the MO methods used are briefly discussed.