Magnetorheological (MR) fluid devices have been promoted as one of the most promising devices for the next intelligent applications. MR device has been implemented as a smart actuator for automotive advanced suspensions, intelligent prosthesis, earthquake resistant structure, and many others. This book provides a walk-trough process in designing one of the most important MR device, the MR valve. Although the case study discussed in this book is a valve, the standard methodology used in this book can be used in the design process of other types of MR devices such as dampers, brakes and clutches. The process on modeling the MR valve in both analytical and data driven approach are also provided in this book. Further, the authors wish that this book will help students, researchers and designers in the development process of various MR based devices.