The significance of developing a responsive user interface lies in its ability to provide a seamless experience across various devices and screen sizes. A responsive design automatically adjusts layout, images, and navigation elements, ensuring usability on smartphones, tablets, and desktops. This enhances user engagement, reduces bounce rates, and improves accessibility, as more users access the web through mobile devices. Additionally, a responsive UI positively impacts SEO, as search engines favor mobile-friendly websites, ultimately driving traffic and improving overall site performance.