This book consists of 14 chapters. Chapters 2 and 3 are devoted to the dynamics of active structures, the open loop transfer functions are derived from the constitutive equations, the discussion includes active trusses with piezoelectric struts, and beams and shells with embedded laminar piezoelectric actuators and sensors. Chapters 4 and 5 discuss the virtues of collocated actuator/sensor configurations and how they can be exploited to develop active damping with guaranteed stability. Chapter 6 addresses vibration isolation for one and 6 d.o.f.. Chapter 7 discusses optimal control for SISO systems with symmetric root locus. Chapter 8 discusses the design tradeoffs for SISO systems in the frequency domain, including the Bode amplitude/phase relationship. Chapter 9 provides a more general discussion of optimal control using of optimal control using the Riccati equation, spillover is examined. Chapters 10 and 11 review briefly the concepts of controllability, observability and stability. Chapter 12 discusses the semi-active control, including some materials on magneto-rheological fluids. Chapter 13 describes various practical applications to active damping, precision positioning and vibroacoustics, and chapter 14 discusses the active damping of cable- structures.