Attribution is the set of rules that decides which ad interaction gets credit for a conversion. Click-through attribution credits conversions that occur after a user clicks an ad, while view-through attribution credits conversions that occur after an impression even if the user never clicked. Last-click attribution is the simplest model: it credits 100% of a conversion to the most recent eligible click before the conversion. Last-click is easy to implement but can be misleading because it over-credits bottom-funnel touchpoints and under-credits channels that create demand earlier in the journey.
Because attribution models are heuristics rather than ground truth, sophisticated advertisers measure incrementality: the causal lift in outcomes caused by ads, compared with what would have happened without them. Incrementality is typically measured through holdout tests, geo tests, split tests, or randomized experiments that include a control group. These designs isolate the true contribution of advertising and help allocate budget more rationally than rule-based attribution alone.
The technical plumbing that makes attribution work includes UTM parameters, which are appended to URLs to pass campaign, source, and medium data into analytics; tracking pixels, which are JavaScript tags that record events such as pageviews and conversions and tie them back to ad interactions; and server-side conversion tracking, in which conversion events are sent from the advertiser's own server to ad platforms. Server-side tracking is increasingly important because browser restrictions and ad blockers can cause client-side signals to be lost, degrading measurement and optimization.