What is populism?

Populists tend to frame politics as a battle between the virtuous 'ordinary' masses and a nefarious or corrupt elite – and insist that the general will of the people must always triumph. The Guardian is adopting the classic definition of populism proposed by political scientist Cas Mudde. Populism, he says, is often combined with a "host" ideology, which can either be on the left or right.

Populism is as old as democracy itself, but the last 10 years have proven particularly fertile: populist leaders now govern countries with a combined population of almost two billion people, while populist parties are gaining ground in more than a dozen other democracies, many of them in Europe.

Against this backdrop, the Guardian is launching a six-month investigative series to explore who the new populists are, what factors brought them to power, and what they are doing once in office.