Susan M. Gass is an American applied linguist and University Distinguished Professor at Michigan State University, where she has been based for decades in the Second Language Studies program. Her career has centred on input, interaction, and the methodology of SLA research itself.
Gass's contribution has been to take the interactionist tradition seriously enough to systematize it. Where Long proposed the mechanism, Gass helped specify it, test it, and make it teachable to graduate students. Her introductory textbook with Selinker has trained more than one generation of SLA researchers.