Publishers need to sell their ad space efficiently. A supply-side platform, or SSP, connects a website's inventory to multiple exchanges and demand sources at once. Instead of negotiating with each buyer, the publisher lets software handle the auctions.

The SSP maximizes revenue by routing each impression to the highest bidder. It also applies rules about which advertisers can buy, what formats are allowed, and what minimum prices apply. Premium publishers use SSPs to protect their brand while still selling programmatically.

Core SSP functions

• Connecting to multiple ad exchanges
• Managing floor prices
• Enforcing brand safety rules
• Reporting on revenue and fill rates

The mirror image is the demand-side platform, which represents buyers. Both sides meet at the ad exchange, where the actual transaction happens in milliseconds.