Representations of semisimple Lie algebras in the BGG category O

"This is the first textbook treatment of work leading to the landmark 1979 Kazhdan-Lusztig Conjecture on characters of simple highest weight modules for a semisimple Lie algebra g over C, The setting is the module category [O] introduced by Bernstein-Gelfand-Gelfand, which includes all highest weight modules for g such as Verma modules and finite dimensional simple modules. Analogues of this category have become influential in many areas of representation theory."--Jacket.