This Companion Textbook supplements the ActivEpi CD-ROM, sold separately. The ActivEpi CD-ROM provides a multimedia presentation of concepts, commonly taught in an introductory epidemiology course. ActivEpi mixes a full array of media to motivate, explain, visualize and apply epidemiological concepts. Virtually all of the material on the ActivEpi CD-ROM is included in the Companion Textbook. Because individuals differ in their learning skills, the ActivEpi CD-ROM and the ActivEpi Companion Textbook offer readers different but related options on how to learn epidemiology. The Textbook can be used as a hardcopy reference of the textual materials contained on the CD-ROM, as a resource for the practice exercises, as a general reference, or even a self-contained textbook. ActivEpi includes 15 lessons and over 50 hours of content via more than 250 launchable activities and homework exercises. It can be used in a variety of teaching formats: distance learning, self-paced learning, on-campus courses, and short courses. For the latest additions to ActivEpi, visit David Kleinbaum's website.