The significance of responsive web design in modern web development lies in its ability to create websites that adapt seamlessly to different screen sizes and devices. This approach enhances user experience, making sure that content is easily accessible whether viewed on a desktop, tablet, or smartphone. By using flexible grids, images, and media queries, responsive design improves SEO performance as search engines prioritize mobile-friendly sites. Furthermore, as mobile internet usage continues to rise, having a responsive site is vital for retaining visitors and minimizing bounce rates, contributing to overall site effectiveness and user satisfaction.