April 21, 2015 – New Search Ranking Rules Favor Mobile Responsive Sites
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. Consequently, users will find it easier to get relevant, high quality search results that are optimized for their devices.
Read the whole Google announcement.
You can test your site(s) on a Google test page : Mobile-Friendly Test
BTW – I’ve written earlier on this topic: Are Businesses in My Hometown Mobile Ready?