Auctions are online marketplaces where buyers place real-time bids for publishers’ ad inventory (impressions).

Auctions are the core function of any supply-side platform (SSP). The demand-side platform (DSP) provides the bidding functionality while the SSP hosts the auction.

Available ad inventory is posted on the SSP, bids are received via DSPs, and the SSP provides the decision-making process on who wins the bid. Auctions can operate on a first-price or second-price basis and can be open or private (invitation-only).