This monograph consists of new results on the stabilization of time-delay systems using PID controllers. The main thrust of the book is the design of PID controllers for time-delay systems, for which the authors have obtained some important specifications, insights and new design techniques. Among the problems considered in this book, an important one is that of stabilizing a first-order plant with dead time using a PID controller. Based on Pontryagin results, this problem is analyzed and solved for both open-loop stable and unstable plants. The solution, although numerically based, allows one to compare several PID tuning techniques based on first-order models with time delays in terms of their resilience to controller parameter perturbations. Another problem that is analyzed and solved in this book is that of stabilizing a general linear time-invariant plant with dead time using a PID controller. The numerical procedure presented allows the engineer to determine for a fixed value of the proportional gain, the region of stabilizing integral and derivative gains for the given plant. The results presented will find widespread applications, specifically in the development of computationally efficient tools for PID controller design and analysis.