Every time a webpage loads with an ad on it, something has to decide which ad to show and then count the impression. That something is an ad server. It is unglamorous infrastructure, but nothing digital runs without it.

Publishers use ad servers to manage their inventory, set priorities, and rotate creatives. Advertisers use them to traffic campaigns, apply targeting rules, and cap how often a user sees the same ad. Both sides get reporting on impressions, clicks, and conversions.

Typical functions

• Delivering creative files to the right slot
• Counting impressions and clicks
• Applying frequency caps and targeting
• Generating performance reports

Ad blockers and privacy rules have complicated the job. Servers now lean on first-party data and contextual signals because third-party cookies are fading.