Current research in High Energy Physics focuses on a number of enigmatic issues that go beyond the very successful Standard Model of particle physics. Among these are the problem of neutrino mass, the (as yet) unobserved Higgs particle, the quark-gluon plasma, quantum aspects of gravity, and the so--called hierarchy problem. Satisfactory resolution of these important questions will take much research effort in both theory and experiment. The Science & Engineering Research Council, Department of Science & Technology has sponsored a series of SERC Schools in Theoretical High Energy Physics over the past several years, to provide instruction and training to graduate students working for research degrees. This book is an outcome of the schools held at the Saha Institute of Nuclear Physics, Kolkata in 2000, and at the Harish-Chandra Research Institute, Allahabad in 2001. Based on lectures by active researchers in the field---Rajiv Gavai, Debashis Ghoshal, Dileep Jatkar, Anjan Joshipura, Biswarup Mukhopadhyaya, Sreerup Raychaudhuri, Saurabh Rindani, Ashoke Sen and Sandip Trivedi---the nine chapters comprising the book deal with a number of topics that range from the fundamentals of the field, to problems and questions that are at the very forefront of current research. This volume will thus be useful to the advanced graduate student who has familiarity with quantum field theory, the Standard Model, and the general theory of relativity, and will also provide a useful reference for working scientists.