Lie Groups and Lie Algebras II: Discrete Subgroups of Lie Groups and Cohomologies of Lie Groups and Lie Algebras by A.L. Onishchik
A systematic survey of all the basic results on the theory of discrete subgroups of Lie groups, presented in a convenient form for users. The book makes the theory accessible to a wide audience, and will be a standard reference for many years to come.