Geometric survey of subgroups of mapping class groups
arXiv:math/0702428
Abstract
The theme of this survey is that subgroups of the mapping class group of a finite type surface S can be studied via the geometric/dynamical properties of their action on the Thurston compactification of the Teichmuller space of S, just as discrete subgroups of the isometries of hyperbolic space can be studied via their action on compactified hyperbolic space.
26 pages. To appear in Handbook of Teichmuller Theory, Volume 1, ed. A. Papadopolous, European Math. Soc. 2007