To what extent is human cognition augmented by language? Does language only enhance communication, with words acting as triggers for nonlinguistic concepts? Or does language play an active role in the very ability to construct and manipulate those concepts? I will present a series of experiments showing that language has pervasive and surprising effects on a range of cognitive abilities, such as learning new categories, deploying knowledge about familiar categories, and even basic perception: Hearing a word can literally change what one sees. I will conclude by discussing the “design features” of words that make them especially useful for constructing and manipulating mental representations.