Hall algebras and Donaldson-Thomas invariants

This is a survey article on Hall algebras and their applications to the study of motivic invariants of moduli spaces of coherent sheaves on Calabi-Yau threefolds. It is a write-up of my talks at the 2015 Salt Lake City AMS Summer Research Institute and will appear in the Proceedings. The ideas presented here are mostly due to Joyce, Kontsevich, Reineke, Soibelman and Toda.