To build on what hathawsh said: 1. Virtual DOM -- but this also includes DOM diffing, which makes it extremely efficient to re-render "the entire app" whenever

To build on what hathawsh said: 1. Virtual DOM -- but this also includes DOM diffing, which makes it extremely efficient to re-render "the entire app" whenever a change happens (because you're not actually rendering it all but you largely don't have to know that). 2. JSX -- but unlike HTML this is just syntactic sugar for the underlying API. It may look like someone got HTML in your JS but it's really just syntax for nesting components and the rest is plain old JavaScript (compared to HTML templates where you have to learn a proprietary template language to do the same things you can already do in JS). 3. Unidirectional (one-way) data flow with pure components. This isn't enforced by React itself but if you stick to constructing your components this way (which companion libraries like Redux encourage you to do), your entire application becomes easier to reason about because you can think of your React code as one giant render function. A lot of these concepts have appeared in other libraries and frameworks but prior to React we used to think that Angular 1's two way bindings were the holy grail (despite the countless complexities it brought in real applications).