Handel and Mosher develop a decomposition theory for subgroups of Out(Fn) that generalizes the decomposition theory for individual elements of Out(Fn) in the work of Bestvina, Feighn, and Handel, and that is analogous to the decomposition theory for subgroups of mapping class groups in Ivanov's work. After introducing subgroup decomposition, they cover geometric models, a relative Kolchin theorem, weak attraction theory, and relatively irreducible subgroups. Annotation ©2020 Ringgold, Inc., Portland, OR (protoview.com)