Much like the Chupacabra or Loch Ness Monster, you may have heard of ad exchanges but have no idea what they are.

An ad exchange is a company that brokers online advertising by bringing publishers and advertisers together on a website where they can participate in auctions for ad space. An ad exchange is a marketplace -- set up much like a NASDAQ exchange for online ads -- where publishers and advertisers can find and execute advertising transactions. Ideally, exchanges provide a system of controls to keep the community safe from harmful, objectionable content as well as create an open development structure to encourage innovation in the industry.

If you've considered working with an ad exchange but have no idea where to start, who the major players are, what they offer or how they differ, there's no better place to start than here.

We did some of the heavy lifting for you and reached out to the top ad exchanges for a head-to-head comparison of what makes them tick and how they can be successful for your brand as a broker for online ad inventory.

If you have questions that aren't addressed in our guide, iMedia invites you to leave them in our comments section. If you're an ad exchange that would like to be included in future crib sheets, please contact me.

Now let's take a look.

Author notes: Nanette Marcus is an editor at iMedia Connection.  Read full bio.