Comparative linguistics and grammaticalization theory both belong to the broader category of historical linguistics, yet few linguists practice both. The methods and goals of each group seem largely distinct: comparative linguists have by and large avoided reconstructing grammar, while grammaticalization theoreticians have either focused on explaining attested historical change or used internal reconstruction to formulate hypotheses about processes of change. In this collection, some of the leading voices in grammaticalization theory apply their methods to comparative data (largely drawn from indigenous languages of the Americas), showing not only that grammar can be reconstructed, but that the process of reconstructing grammar can yield interesting theoretical and typological insights.