This book addresses issues concerning the scale and diversity of an increasingly prosperous but as yet rather unsecure Internet. It explains how digital certificates establish trust for the Internet and how trust enables applications to operate safely, as intended by their original designers. We have selected topics that range from introducing the fundamentals of security and digital certificates to providing coverage of advanced material on certification practice statements and computer security management. Often, we introduce a concept early on and revisit it later in the book, each time analyzing and explaining it from a different perspective.