Chapter 24, Handling Application State, discusses how application state is important for any React application, web or mobile. This is why understanding libraries such as Redux and Immutable.js is important.

Chapter 25, Why Relay and GraphQL?, explains that Relay and GraphQL, used together, is a novel approach to handling state at scale. It’s a query and mutation language, plus a library for wrapping React components.

Chapter 26, Building a Relay React App, shows that the real advantage of Relay and GraphQL is that your state schema is shared between web and native versions of your application.