Now with solutions to selected problems, this bestselling textbook presents the tools of combinatorics from an applied point of view. It focuses on three basic problems of combinatorics: counting, existence, and optimization problems. The text contains many examples from the biological, computer, and social sciences, including disease screening, genome mapping, satellite communication, search engines, telecommunications traffic, web data, sound systems, oil drilling, dynamic labor markets, data mining, and distributed computing. It also offers numerous references to the literature of combinatorics and its applications that enable readers to delve more deeply into the topics.