Most people have heard of the concept of infinity, but pinning down a definition for it can be tricky. One might say that $$\infty$$ is larger than any number you can think of, but in that case, what can we say about $$\infty+1$$? Is there only one type of infinity, or can you make something that is strictly bigger than $$\infty$$? Similarly, is it possible to make something infinitely small? Another line of questioning comes from asking why should we care? If it is not possible, for example, to own $$\infty$$ dollars, then what use is infinity in the first place? We will discuss applications in physics where using infinity actually simplifies our problems. By the end of this course, you should have a sense of how infinity is a real and useful thing.