Some long-standing problems in delay systems are given an elegant and systematic new treatment in this book, which features a methodology developed by the authors. The authors' approach deals with control of nonlinear systems in the presence of long delays, with large and rapid variation in the actuation or sensing path, or in the presence of long delays affecting the internal state of a system. The material is based on predictor feedback and infinite-dimensional backstepping transformations for linear systems, and the authors guide the reader from the basic concepts all the way through to nonlinear systems with state-dependent delays on the input as well as on system states. All control designs are given by explicit formulae, making the book especially useful for engineers who are concerned with actual implementations, and are accompanied by Lyapunov-based analysis for establishing stability and performance guarantees.