This document introduces Reflex, a new component framework for building user interface controls. Reflex is designed to address the need for more customizable and flexible components to work across diverse screens and devices. It takes a new approach to component design that combines skinning and behavior to allow components to be visually and interactively customized. The framework provides core components and follows principles of pay-as-you-go and composability to create reusable, lightweight UI building blocks.