Adapt.js is a lightweight (831 bytes minified) JavaScript file that determines which CSS file to load before the browser renders a page. If the browser tilts or resizes, Adapt.js simply checks its width, and serves only the CSS that is needed, when it is needed. A potential drawback of Adapt.js is the possibility of a brief flash of unstyled content as a new stylesheet is being fetched (think of it as “Ajax” for CSS). I have done my best to mitigate this by keeping CSS files small (3 KB). It is worth noting this is a proposed, not prescribed, approach to a problem with multiple solutions. Other methods include: Build a separate site for mobile. Or, use media queries to adjust layout, with a polyfill for older browser support, and conditional Internet Explorer comments for Windows phones. Also a factor is how to handle multiple image resolutions without adding file size. Filament Group is advocating context aware image sizing.