It was founded by a comedian and one of their slogans has been 'vaffanculo' or 'go screw yourself'
Italy's anti-establishment Five Star movement (M5S) has achieved a major breakthrough by winning Rome's mayoral election.
The country's second biggest political force is a hard-to-describe broad church, resisting traditional categories of left and right and defined by its anti-establishment stance.
How did it emerge?
M5S was founded by comedian Beppe Grillo in 2009 as an alternative to established politicians and institutions in a country long blighted by corruption.
It eschewed traditional political channels and the media for civic lists and citizen meet-ups, embracing the expletive "vaffanculo" ("go screw yourself") as a political slogan.
Co-founder Gianroberto Casaleggio, a communications entrepreneur considered the M5S's "guru" until his death in April, created a series of online platforms for "direct democracy", and all the party's candidates are elected online.
What does it want?
The party is built on the dual pillars of mistrust of traditional politics and honesty of its members.
It wants greater transparency, a reduction in political salaries, action in favour of the environment, a referendum on the euro, growth measures for small and medium businesses and free Internet for all.
Populist or leftist?
Although based on a similar mass rejection of the establishment as Spain's Podemos and Greece's Syriza, the M5S is not left-wing or anti-austerity.
Grillo called for a "clamp-down" on humanitarian visas for asylum seekers in 2014. And the movement withdrew its support for gay civil unions in parliament earlier this year at the last minute, despite 80 per cent of its voting members favouring the bill.
A government in waiting?
The M5S made a sensational debut by scooping 25 per cent in the 2013 general election, becoming the second biggest political force in Italy behind the centre-left Democratic Party (PD) in one swoop.
It hopes Rome will be a platform for a tilt at national power but its party organisation remains weak: it presented candidates for just 18 per cent of the 1,368 municipalities in the latest elections.
How it operates:
M5S's political novices, dubbed "Grillini" after founder Grillo, are struggling to make their voices heard in parliament: the movement refuses to form any alliances with its opponents and cold-shoulders mainstream media.
Locally elected representatives are bound by a code of conduct that requires them to seek permission from the top for every important decision.
The party's anti-corruption banner has also been blackened by allegations it struck deals with local mobsters in Naples in southern Italy, while preliminary probes have been launched into the M5S mayor of Parma in the north for abuse of office and his counterpart in coastal Livorno for fraud.
Who follows the joker?
Although he has officially distanced himself from politics and returned to the stand-up circuit, outspoken Grillo drew bad press last month with an off-colour joke on London's new Muslim mayor and his blog is still perceived as a voice box for the movement.
Smart-suited Luigi Di Maio is tipped to replace him as the movement's figurehead but Rome's newly elected mayor Virginia Raggi is now equally well-placed to assume the role.