The technology essential for creating responsive web designs is CSS (Cascading Style Sheets), particularly through the use of media queries. CSS allows developers to adjust the layout and presentation of webpages based on different screen sizes and devices. Responsive design ensures that websites provide an optimal viewing experience across desktops, tablets, and smartphones, enhancing usability. Additionally, frameworks like Bootstrap offer pre-built responsive design components, streamlining the development process while maintaining consistency and visual coherence across various platforms.