20K01 Finite abelian groups
20K10 Torsion groups, primary groups and generalized primary groups
20K15 Torsion-free groups, finite rank
20K20 Torsion-free groups, infinite rank
20K21 Mixed groups
20K25 Direct sums, direct products, etc.
20K27 Subgroups
20K30 Automorphisms, homomorphisms, endomorphisms, etc.
20K35 Extensions
20K40 Homological and categorical methods
20K45 Topological methods [See also 22A05, 22B05]
20K99 None of the above, but in this section