Core Web Vitals are Google's official performance benchmarks for user experience, consisting of three measurable metrics: Largest Contentful Paint (LCP), which tracks how long your main content takes to render (target: under 2.5 seconds); Interaction to Next Paint (INP), which replaced First Input Delay in March 2024 and measures how quickly your page responds to all user interactions throughout the session (target: under 200ms); and Cumulative Layout Shift (CLS), which quantifies unexpected layout jumps that make users accidentally click the wrong thing (target: under 0.1). These aren't lab-only numbers. Google evaluates them using the Chrome User Experience Report, meaning real visitors on real devices in real network conditions. A site might pass in your Toronto office on fibre but fail for mobile users in rural BC on LTE. The 75th percentile of your field data determines whether you pass or fail each metric. Core Web Vitals became a confirmed ranking factor in June 2021, though Google has repeatedly stated the weight is modest compared to relevance and content quality. In practice, we see them matter most when two pages are otherwise comparable in authority and intent match. They also directly impact conversion rates—Amazon found every 100ms of latency cost them 1% in sales, and similar patterns hold across e-commerce. Common failures we fix: LCP issues from unoptimized hero images or render-blocking CSS, INP problems from heavy JavaScript execution or third-party tag managers, and CLS from ads or embeds loading without reserved space. Server response time under 600ms and proper image dimension attributes solve most LCP and CLS issues respectively. At Ottawa SEO, we run monthly Core Web Vitals audits through PageSpeed Insights and Search Console's CWV report, prioritizing fixes by traffic volume and business impact. A blog post with layout shift gets lower priority than a product page with slow LCP. The goal isn't perfection across 500 pages—it's passing thresholds on pages that actually drive revenue or rankings.