The Garda Commissioner Martin Callinan says there are around 25 criminal gangs operating in Ireland.
Callinan has told the Oireachtas Justice Committee that there is a gang working out of every garda jurisdiction in the country - but most are centred in Cork, Dublin, Limerick and Sligo.
He says Irish criminal organisations continue to forge links with international gangs - particularly in Holland and Russia - and that drug trafficking is the catalyst for almost all of the serious crime issues in Ireland.
Commissioner Callinan says it's difficult to say how many people are involved in organised crime: "For instance, you could have a particular group involved in conducting in armed robberies, for the purpose of securing cash to buy drugs or whatever.
"They might farm out certain duties, like stealing cars, to other criminals further down the food chain. They cross over, so it's particularly difficult to put numbers on these people."