Book excerpt: This edited volume, based on papers presented at the 2017 Georgetown University Round Table on Language and Linguistics (GURT), approaches the study of language variation from a variety of angles. Language variation research asks broad questions such as, "Why are languages' grammatical structures different from one another?" as well as more specific word-level questions such as, "Why are words that are pronounced differently still recognized to be the same words?" Too often, research on variation has been siloed based on the particular question—sociolinguists do not talk to historical linguists, who do not talk to phoneticians, and so on. This edited volume seeks to bring discussions from different subfields of linguistics together to explore language variation in a broader sense and acknowledge the complexity and interwoven nature of variation itself.