The main goal of bringing out this book is to make available to the students a book that contains the subject matter that they need to know. All the concepts are explained in a simple and lucid style and in a compact way. This book begins with an introduction to computer networks, and then necessary aspects of signals are presented. Then all the layers of the OSI and TCP reference models are well explained in depth with necessary diagrams. Other important aspects like “Network Security, WWW, Multimedia, Data Compression”, are also covered.