20XX GROUP THEORY AND GENERALIZATIONS
 2000 General reference works (handbooks, dictionaries, bibliographies, etc.)
 2001 Instructional exposition (textbooks, tutorial papers, etc.)
 2002 Research exposition (monographs, survey articles)
 2003 Historical (must also be assigned at least one classification number from Section 01)
 2004 Explicit machine computation and programs (not the theory of computation or programming)
 2006 Proceedings, conferences, collections, etc.
 20Axx Foundations
 20Bxx Permutation groups
 20Cxx Representation theory of groups [See also 19A22 (for representation rings and Burnside rings)]
 20Dxx Abstract finite groups
 20Exx Structure and classification of infinite or finite groups
 20Fxx Special aspects of infinite or finite groups
 20Gxx Linear algebraic groups and related topics (For arithmetic theory, see 11E57, 11H56; for geometric theory, see 14Lxx, 22Exx; for other methods in representation theory, see 15A30, 22E45, 22E46, 22E47, 22E50, 22E55)
 20Hxx Other groups of matrices [See also 15A30]
 20Jxx Connections with homological algebra and category theory
 20Kxx Abelian groups
 20Lxx Groupoids (i.e. small categories in which all morphisms are isomorphisms) (For sets with a single binary operation, see 20N02; for topological groupoids, see 22A22, 58H05)

20Mxx Semigroups
(1)
 20Nxx Other generalizations of groups
 20Pxx Probabilistic methods in group theory [See also 60Bxx]