Housing protests are taking place at 20 locations around the country including Cork, Waterford, Limerick, Sligo, Drogheda and Bray.
The largest demonstration is at the Garden of Remembrance in Dublin.
More than a thousand people are believed to have gathered for the demonstration in the city centre.
One protester explained that she hoped today's demonstrations will "hopefully get people talking and get more collective action".
Demonstrators marched down O'Connell Street, and a sit-down protest was staged at O'Connell Bridge - leading to traffic disruption along the quays.
The housing activist group, Take Back The City, is behind today's events.
Organisers say the housing crisis in an 'island-wide' issue.
Another property has also been taken over in Dublin as part of the 'national day of action', with People Before Profit saying activists have occupied Glebe House in Crumlin for the next 24 hours.