React Native is a framework for writing iOS and Android apps in JavaScript using React's component model. Instead of writing Objective-C/Swift and Java/Kotlin separately, you write JavaScript once and it compiles to native code on both platforms. This "learn once, write anywhere" approach saves months of duplicate development. React Native apps run on the native runtime (not a WebView), so they have access to device sensors, native APIs, and near-native performance. The bridge between JavaScript and native code handles the heavy lifting.