The technology essential for creating responsive web designs is CSS (Cascading Style Sheets) combined with HTML and JavaScript. Responsive web design allows websites to adapt to various screen sizes and devices, providing an optimal user experience. By using CSS media queries, developers can apply different styles based on the device's characteristics, such as screen width. This approach ensures that content is accessible and visually appealing on desktops, tablets, and smartphones. Responsive design enhances usability, which is critical for engaging and retaining users in an increasingly mobile-first world.