Google Analytics 4 tracks how people interact with your website and mobile apps in a unified property. Unlike Universal Analytics, which expired in July 2023, GA4 uses an event-based model that captures every user action as an event—page views, clicks, video plays, purchases, form submissions. This gives you granular data about what users actually do, not just which pages they land on. GA4's core use cases include measuring traffic sources to see which channels drive real conversions, tracking ecommerce transactions and revenue attribution, analyzing user paths through your site to identify drop-off points, and building audiences for remarketing. The platform reports on acquisition, engagement, monetization, and retention in separate hubs, making it easier to answer specific business questions. The tool was built for a privacy-first world. It uses predictive modeling to fill gaps where cookies fail or users opt out, which matters as third-party cookies disappear and privacy regulations tighten across Canada and globally. GA4 also connects to Google Ads for conversion import, lets you set up custom events without code through the interface, and offers cross-domain tracking when you run multiple properties. At Ottawa SEO, we use GA4 to diagnose why organic traffic doesn't convert, identify which blog posts drive leads versus vanity pageviews, and prove ROI on technical SEO fixes. For a 60-domain portfolio client, we tracked a 34% bounce rate drop after site speed improvements by comparing GA4 engagement metrics month-over-month. The engagement rate metric—sessions with meaningful interaction—replaced bounce rate as the primary quality signal. Key limitation: GA4's learning curve is steep. The interface hides useful reports behind Explore templates, and default reports often lack the dimensions you need. Plan to spend 8–12 hours learning the platform or hire someone who already knows it. Also, GA4 sampling kicks in above 10 million events per property per query, which affects larger sites. For our 500+ domain portfolio, we segment properties to stay under thresholds and maintain accurate reporting.