The NCT is a National Car Test carried out on all cars in Ireland that are over 4 years old. It is carried out every 2 years. From June 2011 - cars over 10 years old will require an NCT test every year.
The company responsible for carrying out the NCT tests is Applus - they took over from SGS in 2010.

If you can't get an appointment for an NCT within 4 weeks - you may be able to get a FREE NCT TEST
Car owners are not issued with a reminder that they are due an NCT - the onus is on the car owner. There does not appear to be any central database of which cars have no NCT certificate - it looks like the Gardai just have to try and spot them! In the UK - the police have access to a database of all the cars without MOT- and number recognition computers can alert them to suspect cars. No such thing in Ireland though.

The NCT test is more concerned with safety and gas emissions than with road worthiness. Exhaust fumes are tested - as are headlight alignment, seat belts, tyres, brakes, windscreen.
NCT testing centres just carry out the test. If the car fails - it needs to be repaired at a garage or by the owner.
The testing fee is currently €50 euro. A retest costs €28 - but must be booked within 21 days of the original NCT test otherwise you pay the €50 again. Minor failures such as registation plates or wiper blades will not require a retest fee.

The Vehicle Registration/Licensing Certificate must be brought to the NCT test. Any discrepancies will be notified to the owner/presenter and Vehicle Registration Unit. Even if the vehicle passes all other aspects of the test, a test certificate will not be issued until the discrepancies are corrected.
From Jan 2010 - vehicles registered prior to 1 January 1980 will not be liable to testing.
From January 2010 - the owner/presenter of the vehicle will be required to produce a driving licence or passport, and, if relevant, details of the garage/company on behalf of which the vehicle is presented.

It is up to the owner of a vehicle to ensure that their car has a valid NCT. Drivers without an NCT certificate face a €1,500 fine, but, and from May 2009 drivers will be issued with five penalty points when convicted in court of driving faulty vehicles, driving vehicles without a certificate of road worthiness and for failing to have an up-to-date NCT certificate.

Motorists who fail to address defects identified by the NCT will receive three penalty points if convicted in court.If you lose or misplace your NCT certificate, you can obtain a replacement for a small fee (12.70 euro) by filling out an application form. Call into your local Garda station and obtain form RF134. You must complete the form and it must be stamped and signed by the Gardai. Send the form, your windscreen disk or NCT certificate (whichever part you still hold) and a cheque or postal order for the 12.70 fee payable to Applus