The design concept of compact Magneto-Re heological (MR) directional valve is to use four single MR valves arranged in a Wheatstone bridge circuit concept. An appropriate single MR valve should be suitable for the use in a compact MR directional valve, as well as, it should achieve a good performance. There is no suitable design readily found in pervious literature, also no previous investigation of the configurations in operation and how to operate these configurations were found. Those configurations give more flexibility of hydraulic circuits design depending on the type of applications. The problem to be tackled in this book is about, how to develop and prove of concept of MR directional valve appropriate to be used in hydraulic control system utilizing MR fluid.