Population genetics—the branch of evolutionary biology concerned with understanding how and why populations’ genetic compositions change over time—rests on a well-developed theoretical foundation that draws on genetics, mathematics, and computer science. This textbook provides an approachable but rigorous treatment for advanced undergraduate and graduate students interested in building a quantitative understanding of the genetics of evolution. Existing texts either assume very mathematically advanced readers, or avoid much of the underlying theory, instead focusing on current methods of data analysis. In contrast, develops the theory from first principles. Requiring only confidence in algebra, this self-contained, student-friendly book illustrates the conceptual framework, terminology, and methods of mathematical modeling. It progressively introduces concepts from genetics as needed, while emphasizing biological implications throughout. As a result, readers come away with a deep understanding of the structure of population genetics without needing to master its mathematics.