Experts from wine tasters to radiologists to bird watchers have all undergone perceptual learning—that is, long-term changes in perception that result from practice or experience. Philosophers have been discussing such cases for centuries, from the fourteenth-century Indian philosopher Vedānta Deśika to the eighteenth-century Scottish philosopher Thomas Reid to a great many contemporary philosophers. This book uses recent evidence from psychology and neuroscience to show that perceptual learning is genuinely perceptual, rather than post-perceptual. It also offers a way for philosophers to distinguish between various different types of it, from changes in how one attends to the learned ability to differentiate two properties or to perceive two properties as unified. The book illustrates how this taxonomy can classify cases in the philosophical literature, and then it rethinks several domains in the philosophy of perception in terms of perceptual learning, including multisensory perception, color perception, and speech perception. As a whole, it offers a new philosophical theory of the function of perceptual learning. Perceptual learning embeds into our quick perceptual systems what would be a slower task were it to be done in a controlled, cognitive manner. A novice wine taster drinking a Cabernet Sauvignon may have to think about its features first and then infer the type of wine it is, while an expert identifies it immediately. Perceptual learning frees up cognitive resources for other tasks, such as thinking about the vineyard or the vintage of the wine. All in all, this book explores the nature, scope, and theoretical implications of perceptual learning.