Can we “see” a writer's voice in his/her writing, just as we can hear a person's voice when he/she speaks? What defines an authorial voice in a written text, anyway? How, if at all, can we measure the strength of an author's voice in a written text? To what extent is this concept important to second language (L2) writers and in L2 writing instruction and assessment? Is this concept of voice even teachable to L2 writers? All these questions are what many writing researchers and teachers have been trying to answer, and they together illustrate the complexity of the topic under discussion. Probably due to its elusive nature, voice is often seen as a concept that is at once intriguing and perplexing, indispensable and yet hard to define and operationalize. This entry will seek to offer an overview of the existing scholarly work on this particular topic, including the many discussions about the nature, characteristics, and measurement of voice, the role it plays in L2 writing, and its teachability to L2 writers.