This book describes group sequential stopping rules designed to reduce average study length and control Type I and Type II error probabilities. The authors present one-sided and two-sided tests, introduce several families of group sequential tests, and explain how to choose the most appropriate test and interim analysis schedule. Their topics include placebo-controlled randomized trials, bio-equivalence testing, crossover and longitudinal studies, and linear and generalized linear models. Group Sequential Methods with Applications to Clinical Trials effectively surveys and extends modern methods for planning and conducting interim analyses.