These short notes, already well-known in their original French edition,
present the basic theory of semisimple Lie algebras over the complex
numbers. The author begins with a summary of the general properties of
nilpotent, solvable, and semisimple Lie algebras. Subsequent chapters
introduce Cartan subalgebras, root systems, and linear representations.
The last chapter discusses the connection between Lie algebras, complex
groups and compact groups. The book is intended to guide the reader
towards further study.