New technologies and companies are triggering an unprecedented power shift in online advertising. Real-time bidding on inventory, instantaneous delivery, and ever-deeper audience segmentation and insight have reinvigorated a tired industry. Both advertisers and publishers are feeling newly empowered, along with a host of intermediaries who are attracting a fresh wave of investment. Some early winners are already obvious. But the tune is still playing in this game of musical chairs, and plenty of players from across the value chain will be squeezed out in the end.