Google's search indexing is kind of a big deal - having a high spot in relevant searches for the world's biggest search engine can literally make or break a business. So if you don't want your site to lose its spot, you'd better make sure your website looks good when accessed from a mobile browser. Starting on April 21st, Google's search algorithm will incorporate whether or not a site is "mobile-friendly" when ranking its appearance in search results. Google announced the change on its Webmaster Central blog:
Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal.