If the 21st century is the age of information, then "information theory" must be important, right? But what is information theory and what is it good for? On this episode of Physics with Phil, we talk about the basics of information theory, and how it can be used for applications as varied as telephone calls and making fly embryos. We also discuss the work of May-Britt and Edvard Moser, who discovered grid cells, for which they were just awarded the Nobel Prize in Medicine!