Electronic commerce has become part of the daily routine of consumers and businesses alike on a global level. Millions of secured transactions are made over the Internet every day; new intermediaries have established themselves in both the consumer and business spaces; mobile communication offers an important channel for transactions and payments; cryptocurrencies are pushing the boundary of digital money while web services are gradually replacing EDI (electronic data interface) in business-to-business transactions. Past editions of the book provided a comprehensive and readable survey of the protocols for securing e-commerce and e-payments in consumer and business applications. The current edition preserves this spirit while tracking the changes since September 2003, when the text of the second edition was finalized. Despite the changes, those familiar with the previous editions should still be able to easily navigate the book. First-time readers will find a clear guide to current issues concerning the security of e-commerce, with pointers to more specialized texts listed in the bibliography.