In this appendix we briefly consider some of the basic properties of Lie algebras. There is much more information here than we may need, so we can regard thi~ Appendix as a 'crash course' on Lie algebras. We consider the main steps in the classification of Lie algebras. Some of the information is contained in the simple problems appearing in the text. The language used in this appendix is more mathematical than that in other parts of this book.