Responsive design is an approach to web development that ensures websites and applications automatically adjust their layout, content, and functionality to provide an optimal viewing experience across a wide range of devices and screen sizes. By using flexible grids, images, and CSS media queries, responsive design allows a single website to seamlessly adapt to desktops, tablets, and smartphones, improving usability and accessibility for all users. This technique helps maintain consistency, reduces the need for separate mobile sites, and supports modern user expectations for fluid, device-agnostic browsing.