Facebook has a significant hand in overall online display inventory, accounting for more than 25% of display impressions across the web, according to AdRoll. So it makes sense that when Facebook inserts itself into the retargeting mix, a significant percentage of impressions follow.
The share of retargeted clicks going to Facebook advertising has increased along a similar trajectory to impressions, though the pace has not quite kept up. As of December, Facebook garnered 45% of total retargeted clicks. Other online display retargeting campaigns received the remaining 55% of clicks, despite accounting for only 37% of impressions. Read the rest at eMarketer.