Time-varying signals in power systems require a real- time processing in many applications such as control, protection, and monitoring. Traditional methods based on Fast Fourier Transform (FFT) may lose accuracy in non-stationary conditions. This book is based on a research conducted in Florida State University. In this book the authors provides an alternative method derived from Amplitude Demodulation for real time tracking of time-varying power system signals. It is also shown in this book how an Amplitude Demodulation circuit has been implemented, simplified, and optimized on Field Programmable Gate Arrays (FPGAs). This book will be a good reference to scientists, researchers, and engineers in power quality, FPGA, and digital signal processing.