Maximal green sequences are certain transformations of quivers that were first introduced by Keller in the context of cluster algebras. Later they were generalized to the setting of finite dimensional algebras, where a maximal green sequence is a finite maximal chain in the lattice of torsion classes. More recently, it was shown that these sequences are in bijection with forward hom-orthogonal sequences of bricks in the module category. We use the latter approach to study existence and number of maximal green sequences for string algebras. This is joint work with Al Garver.