In the last two decades, a great effort has been directed towards the development of new smart materials actuators and their corresponding application devices and systems. Currently, some smart materials actuators are commercially applied for several technologies including automotive technology, but some of the smart materials actuators are still far from meeting strict practical requirements such as reliability, cost-effectiveness and robustness against unexpected environment conditions. Therefore, it is timely and appropriate to present recent research on smart materials actuators in terms of material characterization and advanced application systems in a single book. This book describes smart materials actuator technology from materials characterizations to device or system applications. The smart materials introduced in this book include magnetorehological fluid (MRF), magnetorheological elastomer (MRE), electrorheological fluid (ERF), piezoelectric material (PM), shape memory ally (SMA), dielectric elastomer (DE) and ionic polymer (IP). Both physical and chemical characterizations of each smart material are described in details in terms of actuating aspect. In addition, several application devices utilizing each smart material are introduced to provide practical controllability as a potential candidate for new actuators. The application devices introduced in this book include MRF damper for automotive suspension, PM unimorph pump for micro-hydraulic system, MRE flexible structure for vibration control, IP biomimetic micro-robot and SMA civil structure and damper system for vibration attenuation.