It's all too easy assume that your web or mobile app will run on a fast and reliable network with great coverage. The reality for your app's users, though, is often a slow and unreliable network with spotty coverage. What happens when the network doesn't work, or when the device is in airplane mode? You get unhappy, frustrated users. An offline-first app is an app that works, without error, when there is no network connection. An offline-first app can provide a better, faster user experience — both offline and online — by storing content and data locally and then applying progressive enhancement to synchronize with the cloud when a reliable network connection is available. An offline-first approach can be taken with Progressive Web Apps, mobile apps (native and hybrid), desktop apps (e.g. Electron), and Internet of Things (IoT) apps.