Google accounted for $17 billion (39.9%) of net U.S. digital advertising dollars in 2013, and is expected to grow its market share to 40.8% in 2014, according to eMarketer.
Facebook last year was a distant second at 7.4% at $3.17 billion and is projected to grow to 8.2% of the pie this year.
The rest of the pack is expected to stay fairly stagnant, as you can see from the chart.
