Fluid grids, flexible images, and media queries working in harmony. The interface reflows beautifully from 320px to 2560px without a seam.
Pioneered by: Ethan Marcotte
12-column fluid grid with percentage-based widths
Breakpoints: 320 / 768 / 1024 / 1280 / 1536px
Images scale within their containers (max-width:100%)
Typography scales with clamp() or viewport units
Touch targets size up on mobile, density increases on desktop
Responsive UI works best for these industries