This book provides a useful basic introduction to functional analysis for nonexperts in mathematics. It is distinct from most other books on the subject intended for mathematicians. Concepts are explained concisely with visual materials, making it accessible for those unfamiliar with graduate-level mathematics. Two central issues—spectral representation and fixed-point theorem—and how they relate to quantum physics are covered extensively. Researchers and graduate students in physics, mechanical engineering, and information science will benefit from this view of functional analysis.