React-Sizeme is a React library that makes components aware of their width and height, enabling responsive design at the component level. It's designed for React developers who want to create highly reusable components that can adapt to different container sizes. The library offers two usage patterns: a render prop component (SizeMe) and a higher-order component (withSize), with features like performance optimization through throttling/debouncing, support for both functional and class components, and a tiny bundle size.