Likely: These seats are not considered competitive at this point but have the potential to become engaged.
Lean: These are considered competitive races but one party has an advantage.
Toss-Up: These are the most competitive; either party has a good chance of winning.
Democrats currently have 17 seats listed as Lean or Toss Up.
Republicans currently have 27 seats listed as Lean or Toss Up.
NOTE: As a result of decennial reapportionment and redistricting before 2012, many districts listed will undergo minor or major alterations, several will be eliminated, and several new districts have yet to be drawn. Our current 2012 House ratings reflect these considerations, but ratings are subject to dramatic changes as new maps are finalized in 2011 and 2012.
http://www.cookpolitical.com/charts/house/competitive.php