“This textbook can be used by undergraduate and graduate students and can also serve as a comprehensive guide for those seeking an understanding of perturbation techniques and their practical applications. ... The author's pedagogical approach, marked by clarity, coherence, and a student-centered perspective, makes this textbook reader friendly and accessible. References to classical texts at the end of each chapter enhance the educational experience, facilitate continuous learning and support students in further exploration of the subject matter.” (Svitlana P. Rogovchenko, Mathematical Reviews, May, 2024)