Responsive website design allows a website to automatically adapt to different screen sizes and devices like phones, tablets and desktops. It ensures the content is easily readable and accessible for users on any device. Key benefits include flexibility across browsers and devices, easier maintenance as only one website needs updating, improved search engine optimization as the same URL works on all devices, and increased potential for boosting sales. Responsive design provides a customized solution so any user can access a site from anywhere at any time on whatever device they are using.