We are in the age of global communication system. A communication system exchanges information between source and destination. It connects a data source to a data destination through a channel. The most widely used method of communication over distances is through electrical signal, either over cable or free space using radio wave. In data transmission, generally three types of problem arise: - Firstly, A large volume of data has to be handled; secondly, much of the data is very susceptible to error, and thirdly and most importantly, a lack of security exists when a volume of data is transferred from its source to destination if no measure is taken for its security. Security is one of the very important aspects for any organization. The concept of securing messages through cryptography has a long history. This book is basically explaining the fundamental concept of cryptography and some new cryptographic algorithm. This book has several block diagrams to explain the concept of cryptography.