Jetpack Compose is a modern declarative UI toolkit for Android that uses Kotlin to simplify and accelerate UI development with less code. It allows developers to compose UI elements using functions rather than XML views. Compose is built entirely with Kotlin, works across mobile and desktop platforms, and makes it easy to create custom views using a Canvas. While still in alpha, Compose is open source and aims to provide a more productive way to build Android UIs compared to traditional views and XML.