The book "Approximate and Noisy Realization of Discrete-Time Dynamical Systems" by Yasumichi Hasegawa offers a comprehensive investigation of approximation and noise suppression in dynamic systems, encompassing both linear and nonlinear input/output relationships. It is aimed at researchers, engineers, and students specializing in filter theory and system theory. The monograph proposes a novel method that allows for reduction from noisy or noise-free data. This method treats model description as a form of noise or model reduction. To demonstrate the effectiveness of this method, numerous examples of noise reduction and model information reduction are presented. The analysis of state space is highlighted as a central approach to emphasize efficiency in various technological fields.