Vehicles registered in Northern Ireland are assigned a form of dateless registration, introduced in 1903. These registrations follow the format AZ* where AZ is a two- or three-letter code containing either an I or a Z, and * represents a number between 1 and 9999.

As of 2014, the DVLANI has merged with the UK-wide DVLA so that all vehicle records and registration transfers are now handled by the DVLA in Swansea. Now, registration transfers are completed a lot faster and significantly cheaper than they previously were. All Irish registrations are dateless; they do not refer to the year that a vehicle was first registered. This means that an Irish registration can be assigned to any age of vehicle which has been registered in the UK.

Irish registrations are more readily available than Dateless Style registrations and therefore tend to be cheaper in price. They provide the most cost-effective solution to customers wishing to hide the age of their vehicle with cover plates as Northern Irish style registrations can be transferred onto vehicles in England, Wales and Scotland.

Irish registrations are easily identified as they will always contain an I or Z. They are often used as cover plates to hide the age of a vehicle, such as NFZ5329, or CFZ6928. They are also used to spell short names or words that would otherwise be difficult to obtain, such as BAZ, GAZ, or MIA.