SEO for Google's mobile-first index

When Google announced that it would be switching to a “mobile-first” index for its search engine results, it sent waves of panic and confusion through site owners and SEOs alike. What did “mobile-first” mean? How would it affect the search engine results for my company and clients? Why was Google focusing on mobile when non-mobile websites still existed? In this video recording from the International Search Summit Barcelona 2018, Jeff Ferguson explains the definition of mobile-first indexing and how it's different from “mobile only,” why Google is moving towards this strategy, and how to prepare your website on a content, site architecture, and inbound link level for the coming changes.