Core Web Vitals are three specific performance metrics Google uses to quantify user experience: Largest Contentful Paint (LCP) measures loading speed and should happen under 2.5 seconds, First Input Delay (FID) measures interactivity and should be under 100 milliseconds, and Cumulative Layout Shift (CLS) measures visual stability and should stay below 0.1. Google rolled these into its ranking algorithm in June 2021 as part of the Page Experience update. They matter for two reasons. First, they're a confirmed ranking signal. If two pages are roughly equal in content quality and authority, the one with better Core Web Vitals gets the edge. The impact is real but smaller than most SEOs expected—we've seen maybe 3-8 position swings on borderline cases, not wholesale reshuffling. Second, and more important, they correlate directly with conversion rate and bounce rate. A site that takes 5 seconds to load and shifts layout while users try to click loses money, whether Google penalizes it or not. The thresholds are based on 75th percentile field data, meaning 75% of real user visits need to pass. Google measures this through Chrome User Experience Report data, not lab tests. You can check your scores in Google Search Console under the Core Web Vitals report or use PageSpeed Insights for individual URLs. At Ottawa SEO, we treat Core Web Vitals as table stakes, not a magic bullet. Fixing a 6-second LCP down to 2 seconds will help rankings if you're already competitive on content and links, but it won't overcome thin content or zero backlinks. The biggest wins come from optimizing images (convert to WebP, lazy load below the fold), eliminating render-blocking JavaScript, using a quality host with Canadian data centers for Canadian audiences, and reserving space for ads or embeds so they don't shift layout. Most WordPress sites fail CLS because of unspecified image dimensions and third-party scripts that inject content. Fix those first and you'll pass 75% of the battle.