Those who had been closely following the polls were not expecting to wake up to a Conservative majority on Friday morning.
In the days following the election, many have been asking how predictions were so wrong, and the British Polling Council has announced an inquiry.
Here, according to the pollsters themselves, is what happened.
Ex-ICM boss Nick Sparrow:
Writing on Political Betting, Sparrow said that those investigating the polls most look at "sampling measures".
Over the last 23 years it has become more difficult to achieve a sample that is really representative of all voters, and the desire for cheap polls has fuelled the dash to online methods. Assuring sceptics that telephone polls that get usable data from less than 1 in 5 of the numbers dialled, or satisfying those who question the reliability of online panels of voters who actively seek an opportunity to record their vote intentions will be a substantial challenge.