Retargeting (Google calls it remarketing) is showing ads specifically to people who have already interacted with you — visited your site, used your app, watched your video, or joined your email list. Because the audience is pre-qualified, retargeting typically converts at multiples of cold-traffic rates.
Most visitors leave without converting — typical e-commerce converts 2–4% of sessions — and retargeting is the mechanism for a second (and third) conversation with the other 96%. Audiences are built from first-party signals: a site pixel or server-side events (Meta Conversions API, Google's enhanced conversions) recording visitors and actions; customer lists matched by hashed email; and platform-native engagement (video viewers, page engagers, lead-form openers) that requires no cookies at all. Third-party cookie deprecation hurt cross-site display retargeting most; on-platform engagement audiences and server-side events have become the durable backbone.
Segmentation is where retargeting earns or wastes its money. "All visitors, 30 days" is one blunt audience; cart abandoners (high intent, message: friction removal — shipping, returns, support), product viewers (message: the product again, social proof), pricing-page visitors for SaaS (message: objection handling, case study, trial nudge), and past purchasers (message: replenishment or cross-sell, not the thing they just bought) deserve different ads and budgets. Always exclude recent converters — the "burn list" — both to stop annoying customers and to stop ROAS-flattering credit for sales already made.
The failure mode is pressure: small pools hammered at high frequency. Cap frequency (a few impressions per week per user is a sane start), expire windows by purchase-cycle length (7–14 days for impulse e-commerce, 30–90 for considered B2B), and rotate creative — a retargeting pool sees the same ad far more often than a prospecting audience, so fatigue arrives early. Done well, retargeting is the cheapest revenue in the account; done lazily, it is a tax on people who were coming back anyway.
Furniture store: cart abandoners (3 days) see "Still thinking it over? Free delivery & 100-day returns" with the exact sofa; product viewers (14 days) see the sofa plus 4.8★ reviews; buyers are excluded for 60 days, then see a cushions-and-care cross-sell. Frequency capped at 4/week per segment.
Yes — differently. Site retargeting increasingly runs on first-party data and server-side event APIs (Meta CAPI, Google enhanced conversions), and platform-native audiences (video viewers, page engagers, customer lists) never depended on third-party cookies at all.
Partly because it is warm traffic — and partly attribution: retargeting gets credit for buyers who would have returned anyway. Exclude recent converters, cap frequency, and judge it on incremental lift (or at least new-vs-returning splits), not raw ROAS.