An Invitation-Only-Auction is an advertisement bidding procedure in digital marketing that is only accessible to a few selected advertisers.
These auctions, sometimes also referred to as Private Marketplaces (PMPs), are a modification of open auctions. But in contrast to open auctions, publishers can restrict the participation for the bidding process to selected advertisers only using PMPs.
As the name suggests, this kind of auction will only allow advertisers to participate in the bidding process after they have received an invitation from the publisher. The rest is working quite similar to open auctions. Advertisers or Ad Exchanges can set a minimum CPM for each advertiser. Again, the highest bidder will win the impressions.
Invitation-Only-Auctions can be beneficial to both publishers and advertisers. Publishers can generate higher prices for their inventory from selected advertisers with programmatic efficiency. Simultaneously Advertisers get access to premium inventory from trusted publishers also with programmatic efficiency.