SEO and Responsive design
When creating a new website, or updating an existing site, a Responsive design is now a necessity.
What is a responsive design – Very simply the page will adjust with readable text regardless of whether viewed on a 27 inch Imac or a mobile phone.
To check whether your site is considered responsive by Google, you can enter your URL here: https://www.google.co.uk/webmasters/tools/mobile-friendly/
Taken from https://developers.google.com/webmasters/mobile-sites/mobile-seo/configurations/responsive-design?hl=en