Libraries are Sketch documents with components (Symbols, Text Styles, Color Variables, Layer Styles and Artboard Templates) that you can share across all of your other documents — and even across whole teams. You can also enable Libraries per document, keeping at hand just the Libraries you need at that moment.
When you update Components in a Library, documents that use them will get an update notification. You can review those changes and confirm them to make sure you’re always using the most up-to-date Components in your work. You can even apply a Library to a single document, if you prefer.
Libraries are handy for teams who work on designs that share Components like icons, UI elements or branding. But they’re just as handy if you’re an individual. With Libraries, you can quickly insert common Components (like Apple’s iOS UI elements) into your designs and be sure they’re always up to date.