Mobile-First Design is an approach to web development that prioritizes designing for mobile devices before scaling up to larger screens like tablets and desktops. This method recognizes the increasing use of smartphones for internet access and aims to create a seamless user experience on smaller screens. By starting with mobile, designers focus on essential features and content, ensuring that the most important elements are easily accessible. Once the mobile version is complete, they can enhance the design for larger screens, adding more complex features without compromising usability. This strategy helps improve performance and user satisfaction across all devices.