After a brief introduction reviewing the concepts of principal ideal domains and commutative fields, the book discusses residue classes (for example, the integers mog=dulo some number m); quadratic residues; algebraic integers (that is, objects that behave like integers in arbitrary algebraic structures), their discriminant; decomposition, norm, and classes of ideals; the ramification index; and the fundamental theorem of Abelian extensions. The theorems and definitions are carefully motivated, and the author frequently stops to explain how things fit together and what will come next. There are a great many exercises and many useful examples at a