Basically Expo is a set of libraries and tools that make React Native Development easier. It has things as simple as UI components to things as complex as being able to easily test an app on multiple devices. I won’t get into a ton of detail here because you will see how it will be useful when we go through some tutorials below. Just know that it makes cross platform development with React Native easier because it gets by having to use a certain OS for development and testing (for example, to develop native IOS apps you need a MacOS device and an iPhone).