The Congress' inauguration took place in the Indoor Olympic complex in Galatsi, under the slogan "STRONG KKE. Mind-Heart-Organizer of the Workers-People's Struggle for Socialism".
More than 100 Communist and Workers' Parties from all over the world have sent greeting messages for the 21st Congress.
The Thursday's event was concluded with an impressive cultural program.
The works of the 21st Congress continue in the Party's headquarters in Perissos and will be concluded on Sunday 27 June.