From the reviews: "This book provides a thorough study of the observer design problem for certain classes of control systems (i.e., systems with inputs). ... The reference list is exhaustive and the authors present a detailed literature review. ... a mathematician with interest in control theory will gain many things by studying the book ... . To summarize: it is an interesting book with many strong points and the reader will benefit by studying it." (Iasson Karafyllis, Mathematical Reviews, May, 2013) "This is a broad survey of the theory and applications of functional observers, suitable for graduate studies or specialized research stages. The exposition style is attractive and requires a medium level of training in control systems engineering. The presentation of each main theoretical topic relies on a rigorous mathematical foundation and it is accompanied by design algorithm(s) and illustrative example(s)." (Octavian Pastravanu, Zentralblatt MATH, Vol. 1244, 2012)