Google will expand the use of mobile-friendliness as a ranking signal beginning April 21st. This change will make mobile search results more relevant and high-quality for users. Google will assess all websites for mobile-friendliness and include this as a factor in its algorithm. For a site to pass as mobile-friendly, all pages must be optimized for mobile viewing on an individual basis. Sites must also allow Google to crawl CSS and JavaScript files. While responsive design is recommended, other mobile optimization methods will not be penalized. Websites can test mobile-friendliness using Google's mobile-friendly test and mobile usability report in Search Console.