How is responsive design different from adaptive design?

Both responsive and adaptive design attempt to optimize the user experience across different devices, adjusting for different viewport sizes, resolutions, usage contexts, control mechanisms, and so on.

Responsive design works on the principle of flexibility - a single fluid website that can look good on any device. Responsive websites use media queries, flexible grids, and responsive images to create a user experience that flexes and changes based on a multitude of factors. Like a single ball growing or shrinking to fit through several different hoops.

Adaptive design is more like the modern definition of progressive enhancement. Instead of one flexible design, adaptive design detects the device and other features and then provides the appropriate feature and layout based on a predefined set of viewport sizes and other characteristics. The site detects the type of device used and delivers the pre-set layout for that device. Instead of a single ball going through several different-sized hoops, you'd have several different balls to use depending on the hoop size.

Both of these methods have some issues that need to be weighed:

• Responsive design can be quite challenging, as you're essentially using a single albeit responsive layout to fit all situations. How to set the media query breakpoints is one such challenge. Do you use standardized breakpoint values? Or, do you use breakpoints that make sense to your particular layout? What if that layout changes?
• Adaptive design generally requires user agent sniffing, or DPI detection, etc., all of which can prove unreliable.