The basic objective of preparing this textbook is to enable the readers to understand the difficult concepts by following a simplified approach. Also, it is attempted to make the study of the subject a pleasant experience by explaining it in a lucid and organized manner. A lot of illustrations, spectral and block diagrams and detailed derivations have been provided in the development of the material.This book presents the basic principles and analysis involved in Communication Systems. The text provided is basically divided into Analog Communications and Digital Communications and may be broadly divided in to analog communication techniques and their behaviour under the influence of noise. The mathematical techniques involved in this book are at a moderate level. This is keeping in mind the view of the readers, who have a moderate background of differential and integral calculus. Nevertheless, the book provides exposure to some of the sophisticated analytical techniques such as Fourier transform, spectral analysis and the performance of systems in the presence of noise. This text has been developed in an organized manner by including the necessary basic topics in separate chapters.