The Garda Commissioner and the Minister for Justice have launched a new garda operation to try to stop teenagers buying alcohol.
Gardaí will begin sending 15, 16 and 17 year olds into pubs and off-licences to buy alcohol from 1 October.
Minister for Justice Dermot Ahern said the test purchases are designed to ensure publicans and off-licence owners are complying with the law.
A series of guidelines to protect the safety and welfare of the teenagers involved has also been published today.
In a statement this afternoon, Mr Ahern said: 'The test purchasing scheme is intended to protect young people from the all-too-prevalent reality of alcohol-related harm.
'With the commencement of the test purchasing scheme, the Garda Síochána will have an additional instrument in their overall enforcement programme to combat the sale of alcohol to minors.
'I want to stress that the objective of the scheme is to ascertain whether a licensee is complying with the law, not to trap an unwary licensee into committing an offence. The test purchaser must answer all questions about their age truthfully.'
Those convicted of selling alcohol to underage drinkers can have their premises closed down for a week, as well as a €3,000 fine. A second conviction brings a 30-day closure and a €5,000 fine.
The Minister also said that new legislation to tackle online drink sales, particularly to those underage, was being drawn up and would be published by the end of the year.