This book is designed to introduce the reader to the theory of
semisimple Lie algebras over an algebraically closed field of
characteristic 0, with emphasis on representations. A good knowledge of
linear algebra (including eigenvalues, bilinear forms, euclidean spaces,
and tensor products of vector spaces) is presupposed, as well as some
acquaintance with the methods of abstract algebra. The first four
chapters might well be read by a bright undergraduate; however, the
remaining three chapters are admittedly a little more demanding. Besides
being useful in many parts of mathematics and physics, the theory of
semisimple Lie algebras is inherently attractive, combining as it does a
certain amount of depth and a satisfying degree of completeness in its
basic results. Since Jacobson's book appeared a decade ago, improvements
have been made even in the classical parts of the theory. I have tried
to incor- porate some of them here and to provide easier access to the
subject for non-specialists. For the specialist, the following features
should be noted: (I) The Jordan-Chevalley decomposition of linear
transformations is emphasized, with toral subalgebras replacing the more
traditional Cartan subalgebras in the semisimple case. (2) The conjugacy
theorem for Cartan subalgebras is proved (following D. J. Winter and G.
D. Mostow) by elementary Lie algebra methods, avoiding the use of
algebraic geometry.