An attribution model in GA4 is the framework that decides how conversion credit gets distributed across the various channels, campaigns, and interactions a user has before converting. Unlike Universal Analytics which defaulted to last-click attribution, GA4 uses data-driven attribution (DDA) as its standard model. DDA analyzes your actual conversion data to determine which touchpoints statistically contribute most to conversions, then assigns credit proportionally. GA4 offers several attribution models you can compare in reports. Data-driven attribution uses machine learning to compare conversion paths of users who converted versus those who didn't, identifying which interactions actually made a difference. The paid and organic search model gives all credit to the last Google paid or organic search click. The last-click model assigns 100% credit to the final touchpoint before conversion. First-click gives all credit to the initial interaction. Linear spreads credit equally across all touchpoints in the path. The practical difference matters significantly for budget decisions. If you're running awareness campaigns on Meta and conversion campaigns on Google Search, last-click attribution will make your search campaigns look like heroes while Meta gets zero credit, even if Meta initiated the journey. Data-driven attribution would recognize Meta's role if users who saw Meta ads converted at higher rates than those who didn't. At Ottawa SEO, we typically stick with data-driven attribution for clients with sufficient conversion volume (GA4 needs at least 400 conversions per month for DDA to work properly). For smaller sites that don't hit that threshold, GA4 falls back to last-click automatically. In those cases, we'll manually review conversion paths in the Path Exploration report to understand the actual customer journey, because the attribution model isn't telling the full story. The key is understanding that attribution models are interpretive lenses, not objective truth. Your Meta campaign and your SEO work might both be essential, even if only one gets the conversion credit in any single model.