A few weeks ago, Google announced a major change they will soon be making to their search algorithm. You can read the official announcement here. Perhaps the most important statement is the following:
"Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results."
Why is Google making this change?
Approximately 1/3rd of web browsing is now done on mobile devices. Studies have shown (and intuition tells us) that consumers using mobile devices have a much better experience on websites that provide content formatted for mobile devices. Google wants to provide the best search results possible for its users, so they will soon use the mobile-friendliness of a website as a major factor in their search rankings.
This announcement is nearly unprecedented for Google. Typically, Google makes very sparse and vague comments on indicators they incorporate in to their search results. The comments they do make are nearly always after the fact.