As the web landscape becomes increasingly complex, it's becoming extremely important to deliver solid web experiences to a growing number of contexts. Thankfully, responsive web design gives web creators some tools for making layouts that respond to any screen size. We'll use fluid grids, flexible images and media queries to get the layout looking great regardless of the size of the device's screen dimensions.
However, mobile context is much more than just screen size. Our mobile devices are with us wherever we go, unlocking entire new use cases. Because we constantly have our mobile devices with us, connectivity can be all over the board, ranging from strong wi-fi signals on the couch to 3G or EDGE when out and about. In addition, touch screens open new opportunities to interact directly with content and mobile ergonomics lead to different considerations when designing layout and functionality.
In order to create a site that's truly designed for mobile context and not just for small screens, we want to ensure that we tackle the many challenges of mobile development upfront. The constraints of the mobile context force us to focus on what content is essential and how to present that content as quickly as possible. Building fast-loading, optimized experiences mobile first has a trickle down (or up, depending on how you look at it) effect for tablet, desktop and other emerging contexts.