The aim of this paper is to relate Thurston’s metric on Teichmüller space to several ideas initiated by T. Sorvali on isomorphisms between Fuchsian groups. In particular, this will give a new formula for Thurston’s asymmetric metric for surfaces with punctures. We also update some results of Sorvali on boundary isomorphisms of Fuchsian groups. AMS Mathematics Subject Classification: 32G15 ; 30F...