The book "Weighted Littlewood-Paley Theory and Exponential-Square Integrability" provides a comprehensive introduction to Littlewood-Paley theory, which is a fundamental tool of Fourier analysis. This theory has far-reaching applications in various fields, including partial differential equations, signal processing, and probability theory. It allows for the extension of the benefits of orthogonality to situations where it is not directly applicable. By controlling certain oscillating infinite series of functions, a more precise analysis is made possible, which has been significantly refined since the 1980s. The book aims to present the discoveries and methods that led to these advancements in an understandable way, as well as to explain their consequences and applications.