Mobile First is a design and development approach where a website or web application is initially optimized for mobile devices before adapting it for larger screens like tablets or desktops. As more users access the internet primarily through smartphones and tablets, the Mobile First approach ensures that the most important content and functions are accessible and user-friendly on small screens. This approach often leads to a more streamlined, efficient design that ensures faster load times and an improved user experience across all devices. Mobile First contrasts with the older "Desktop First" approach, where designs were created for desktops first and later adapted for mobile devices.