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Algebraic Number Theory [Lang] - mklabgr - 08-17-2026
Algebraic Number Theory
Author: Serge Lang
Series:Graduate Texts in Mathematics, Vol. 110
Publisher: Springer-Verlag
First published: 1970
Serge Lang’s Algebraic Number Theory is a classic graduate-level introduction to the subject, designed to provide the foundations needed for more advanced study in areas such as cyclotomic fields, modular forms, and modern number theory. The book begins with the arithmetic of number fields, developing algebraic integers, ideals, ideal classes, valuations, and related structures. A central theme is that unique factorization, which may fail for algebraic integers themselves, can be recovered by working with ideals. Lang then introduces more sophisticated global and local machinery, including adeles and ideles, which provide a unified framework for studying arithmetic simultaneously at all primes and at the infinite places.
A substantial portion of the book is devoted to class field theory, one of the central achievements of algebraic number theory, describing abelian extensions of number fields through arithmetic information associated with the base field. The later material connects algebraic number theory with analysis through zeta functions and $L$-functions. In treatments associated with the book, Lang also develops analytic topics such as Tate's thesis, the Brauer–Siegel theorem, and Weil's explicit formulas. The presentation is characteristically Lang: concise, abstract, theorem-driven, and mathematically demanding. It is therefore better suited to readers already comfortable with abstract algebra—especially groups, rings, fields, ideals, and Galois theory—than to someone encountering higher algebra for the first time.
The book's importance lies in the way it takes the reader from classical questions about integers and factorization into the structural language of modern number theory. Rather than treating algebraic and analytic methods as isolated subjects, Lang shows how local fields, global fields, class groups, valuations, and analytic functions fit together. It remains particularly valuable as a bridge from graduate algebra to research-level number theory. The Goodreads entry identifies this as Lang's second edition and describes its purpose as supplying the classical algebraic-number-theory background required for further study.
Key takeaways
- Algebraic number fields generalize $\mathbb{Q}$ and provide the natural setting for studying solutions of polynomial equations arithmetically.
- Ideals and ideal classes restore a useful form of unique factorization when ordinary factorization into elements fails.
- Local methods, adeles, and ideles allow arithmetic problems to be analyzed prime by prime and then connected globally.
- Class field theory and zeta/$L$-functions reveal deep links among algebra, arithmetic, analysis, and field extensions.
Goodreads book page