Rural and urban poor, including farmers and industrial workers, make up the movement.
The Red Shirts have been demanding immediate elections, democracy and social justice.
They are refusing to abandon their Bangkok protests until the deputy prime minister, Suthep Thaugsuban, is charged for authorising an army crackdown on 10 April that killed 23 protesters.
The Red Shirts say that, if he is prosecuted, they will leave the area.
They have also accepted prime minister Abhisit Vejjajiva’s timetable for an election on 14 November.
The Red Shirts have put serious pressure on the Thai government, but have failed to build roots in the organised working class.
Their latest concessions to the government could be a missed opportunity to take the struggle in Thailand beyond the reforms offered by the state.