Back in February 2015, Google announced they were rolling out a new algorithm which significantly impacts sites that are not mobile-friendly. By mobile-friendly, they are referring to sites with text that is too large for a mobile device, links that are too close together and not easily clicked from a mobile device, and sites that are not optimized for mobile devices in general. True to their promise, the new algorithm was indeed installed on April 21st and sites that are not mobile-friendly are feeling the wrath. In fact, they have basically been demoted in search results. It’s important to note that the change affects individual pages only and not entire sites. This has some webmasters breathing a sigh of relief.
Those who have ignored the warnings, and haven’t upgraded, will notice a significant drop in mobile traffic. For more information about the algorithm you can check out this article. If you are unsure as to whether or not your site is mobile friendly, Google has provided a mobile-friendly test for your website.