Before we can talk about how we learn, use, and lose language, we need to define what it is, and what it isn’t. Over the centuries, many people have attempted to describe language. In this chapter was ask: what is language? This is a simple enough question although the answer is much more complicated, and intriguing, than it seems at first. The question of “what is language?” isn’t something we can just sum up in a single pithy sentence. Language is a system of communication, but it’s so much more than that. Language is multi-faceted. It involves signs and symbols, smaller and bigger segments, dialects and accents, and also writing and signing. This chapter serves as a primer to introduce us to the basic underlying principles of language sceince, so we can now talk the talk.