The original approach to providing support for mobile devices was to create a separate interface, and have the web site check the user-agent of the device requesting the page to decide which version of a page to send. But with the rise of smartphones as perhaps the most common web accessible device, and the increase in power allowing them to run full web browsers with javascript and web standards support, the responsive approach has become the norm.

A responsive web site sends exactly the same pages to all devices - mobile, tablet, laptop and desktop. It is the device itself which decides how to display the page, based on rules and code that is embedded within the page.

The advantages of this approach are:

• Single set of interface code to create and maintain
  
  
• Richer experience - full feature set (since not using a separate cut-down interface) and same styling and feel as the main site (because they are essentially the same site with some minor tweaks)
  
  
• The interface can be adjusted for a variety of devices of various sizes; for example, tablets can use the chunkier touch-enabled navigation menus while still formatting pages for the larger screen space
  
  
• Same URLs for mobile and desktop - since all clients get the same page, there are no separate URLs for the mobile site; this has search engine benefits and also benefits customers who sync bookmarks between their desktop and mobile browsers (because the same URL will work from both devices, but the pages will format appropriately for each device)