Attribution is a credit-assignment system: last-click, first-click, multi-touch, data-driven. It tells you where a conversion showed up but not what caused it. Incrementality answers the counterfactual using controlled experiments — geo holdouts, audience holdouts, or quasi-experimental analysis. 52% of US marketers now run incrementality tests. Use attribution for daily/weekly tactical work, incrementality for budget allocation decisions, and MMM for strategic long-horizon planning. A 5-phase consulting roadmap: audit your measurement stack, pick two budget questions, design the tests, run them for 4-8 weeks, and build an ongoing experimentation cadence. Reporting outputs: channel-level scorecard with attributed vs incremental ROAS, experiment ledger, and a confidence map.