This resource book, written for mathematics teachers and school library media specialists, provides Web resources that promote critical thinking in the high school mathematics classroom. It consists of 153 activities that address topics in prealgebra, algebra, geometry, precalculus, calculus, probability, and statistics. Each activity has a Uniform Resource Locator (URL) for the activity, a list of mathematical topics addressed by the activity, a summary of the web site of which the URL is a part, a series of discussion questions on the activity, and a list of related sites in the book. Also included are a rationale for the use of technology in education, a guide to using the activities in the book, and a list of the activities sorted by topic. (MM)