This book, aims at doing 2 things: first, to provide the aspirants of UPSC CSE with a one stop solution to their most basic doubts, and second, to give them a solid foundation as they begin preparation. The idea of this book was mine but the execution was not mine alone. It required a lot of support and at times push from many people to finish the work. But, if I were to dedicate this book, it would surely be to, two sets of people, my family and the millions of aspirants. My family has always supported me and stood by me. They have always pushed me to do whatever I wished to and do it well. They also provided guidance whenever I needed it. This book is dedicated to all the aspirants as well, who take this leap of faith every year. I wish and hope that all those who deserve, find the success they are looking for. Thank you.