This book is designed to acquaint the readers with major aspects of e-commerce with particular emphasis on technology such as cryptography, e-payment and mobile payment security. The book presents a layered architecture of e-commerce systems with six layers. The physical layer (the bottommost layer) described first, provides the basic communication infrastructure needed by e commerce. The next layer described is the logical layer consisting of Local Area Networks, the Internet, Intranet, etc. which provide connectivity. The layer above is the network services layer which provides e-mail and World Wide Web applications. Above this is a very important messaging layer of e-commerce which provides facilities for exchanging messages securely using the communication infrastructure. Here various methods of encryption, public key infrastructure and digital signature are discussed. It is also explained as to how the messaging layer is used to exchange structured electronic documents, using XML. The next layer called middleman services layer, describes the design of home page of an organization and elaborates various payment services such as credit card, e cash, smart card, etc. The topmost layer is on applications, namely, B2C, B2B and C2C e commerce which are defined and described at the beginning of the book. As use of mobile phones and mobile network is rapidly increasing, a whole chapter is devoted to explain m-commerce. Of special interest are detailed discussions of Wireless Application Protocol, security issues and payment methods. A complete chapter is also devoted to new developments in multimedia information goods such as e-books, MP3 compressed audio and digital quality video. A unique feature of these goods is the method of delivery which also uses the mobile Internet infrastructure. Finally, the legal framework of e-commerce provided by the Information Technology Act 2000 (and the amended act of 2008) is explained. This book with its numerous student-friendly features is an ideal text for undergraduate and postgraduate students of Computer Science and Information Technology (BSc and MSc), Computer Applications (BCA and MCA), and for undergraduate engineering students of Computer Science and Engineering and Information Technology. Besides, it would be useful to professionals for quickly understanding the basics of e commerce. Key Features : • Gives detailed discussions of security and payment schemes in e-commerce. • Discusses essentials of m-commerce technology including WAP protocol and mobile security. • Discusses e-commerce of multimedia such as e-books, MP3 audio and video on demand. • Provides learning aids such as chapter summaries, over 300 review questions and 350 objective type questions.