Hong Kong student leader Joshua Wong has been charged over protests which led to last year's mass pro-democracy street rallies.
Wong, 18, who became the face of the democracy movement, is already due in court on Friday (local time) for separate charges of obstructing police at an earlier demonstration.
The teenager and other activists have accused the authorities of a witch hunt against those at the forefront of the Umbrella Movement that brought parts of the city to a standstill for more than two months.
Protesters called for fully free elections of Hong Kong's next leader, in the face of a contentious Beijing-backed political reform package in which candidates would have been vetted by a loyalist committee.
That bill was vetoed in June in an unprecedented rebuke to Beijing, leaving the city politically polarised.
Wong was charged on Thursday with "unlawful assembly, and inciting others to take part in an unlawful assembly".
The charges relate to a student protest on September 26 last year during which some climbed into a square which is part of the city government complex.
Wong and other activists were arrested, sparking wider demonstrations which exploded two days later when police fired tear gas to disperse the crowds.
Thousands more took to Hong Kong's streets in the wake of what they saw as heavy-handed policing.