This document discusses responsive design, which delivers a single, flexible design that adapts to different devices. It notes that 50% of US smartphone owners use their phones for shopping-related activities and $158 billion in store sales will be influenced by in-store mobile use. It outlines four approaches: doing nothing, separate desktop/mobile sites, supplementing desktop sites with mobile apps, or using responsive design. Responsive design provides a seamless experience across devices with one code base, is search engine friendly, and offers a future-proof solution, though it requires additional design/development costs. The document advocates starting with a mobile-first or content-focused approach and close collaboration between designers and developers.