The first edition of this book presented the theory of linear algebraic groups over an algebraically closed field. The second edition, thoroughly revised and expanded, extends the theory over arbitrary fields, which are not necessarily algebraically closed. It thus represents a higher aim.

As in the first edition, the book includes a self-contained treatment of the prerequisites from algebraic geometry and commutative algebra, as well as basic results on reductive groups. As a result, the first part of the book can well serve as a text for an introductory graduate course on linear algebraic groups.

The material of the first ten chapters of the new edition is roughly the same as that of the first edition. The arrangement of the material is somewhat different, and a few things have been added, such as the basic facts about algebraic varieties and algebraic groups over a ground field, and an elementary testament of Tannaka’s theorem in Chapter2.

The last seven chapters are new and contain the extension of the theory to algebraic groups over arbitrary fields. Some of the material has not been dealt with before in textbooks—e.g., Rosenlicht’s results about solvable groups in chapter 14, the theory of Borel and Tits on the conjugacy over the ground field of a maximal split torus in an arbitrary linear algebraic group in Chapter 15, and the Tits classification of simple groups over a ground field in Chapter 17.