Google announced in March of 2018 that they would start migrating sites for mobile-first indexing. By now, presumably this process has been complete and mobile-first indexing is the standard for Google's crawlers. You most likely have received an email from Google that mobile-first indexing has been enabled for your site. What does this mean? Historically, Googlebot (Google's web crawler) has visited sites as if it were a desktop user, that is, a user with a relatively large screen with a mouse and a keyboard. With mobile-first indexing, Googlebot is now visiting sites first as a "mobile user" - small screen, no pointing device, touch screen, etc.) So to determine what your pages have to offer, it will first look at those pages as a smartphone, and then as a desktop device. Does this mean there are now separate indexes, one for mobile devices and one for desktops and laptops? No. Google will still use a single index but whatever a mobile user sees is...