In this work the authors develop a decomposition theory for subgroups of $\mathsf{Out}(F_n)$ which generalizes the decomposition theory for individual elements of $\mathsf{Out}(F_n)$ found in the work of Bestvina, Feighn, and Handel, and which is analogous to the decomposition theory for subgroups of mapping class groups found in the work of Ivanov. Les mer