Leading up to the general election we just suffered, the polls were clear - neither Labour nor the Tories would be a majority, and while Tories would likely be a plurality their vote share was roughly the same as Labour. Judging by the current results, the Tories had a 6% advantage in the end result. This isn't the first election which the polls have got significantly wrong recently. Nate Silver points to three other recent ones: the US 2012 presidential (Obama underestimated by 3 points), US 2014 Senate (Republicans underestimated by 4 points) and the Israeli general election (Likud support significantly underestimated). While election polling will always be problematic, the fact that polls seem to uniformly say the same (wrong) thing is somewhat surprising, as each will have its own way of asking things and adjusting for the sample. So what's going on that all the polls are so wrong?