[SOUND] Responsive web design is a collection of techniques for 0:00 building websites that work at multiple screen sizes. 0:03 The [SOUND] scope of responsive design also sometimes includes websites that 0:07 work at different pixel densities, such as traditional [SOUND] screens or 0:12 high DPI screens. 0:16 It all started in May of 2010 when Ethan Marcotte wrote a seminal 0:18 article titled Responsive Web Design on the blog A List Apart. 0:22 You can find a link to the blog post in the notes associated with this video. 0:27 And I highly recommend you take the time to read it. 0:31 Back then, most web professionals would often create a mobile version of their 0:35 site and a desktop version, which means they would have to maintain two 0:39 separate websites, or worse, the site wouldn't work on mobile at all. 0:44 People also used to use JavaScript to detect which browser people were using, 0:50 which is unreliable. 0:54 At first, this seemed like it would be somewhat maintainable, but 0:56 when more phone sizes and then tablets arrived and 1:00 fragmented layouts even further, it quickly became unsustainable. 1:04 Instead, Ethan presented the idea that rather than trying to make a different 1:10 layout for every device and screen size, we should instead create layouts 1:15 that intelligently respond to any device, hence the term responsive web design. 1:20