This volume consists of revised versions of presentations given at a roundtable on “New Directions for Historical Linguistics: Impact and Synthesis, 50 Years Later” held at the 23rd International Conference on Historical Linguistics in San Antonio, Texas, in 2017, as well as an introduction by the editors. The roundtable discussed the evolution of historical linguistics since the 1966 symposium on “Directions for Historical Linguistics,” held in Austin, Texas. Six prominent scholars of historical linguistics and sociolinguistics contributed: William Labov (the only surviving author from the 1968 volume), Gillian Sankoff, Elizabeth Traugott, Brian Joseph, Sarah Thomason, and Paul Hopper (a graduate student assistant at the original symposium).