As part of the United Kingdom, Northern Ireland's currency is the pound sterling (£).
Unusually, individual currency notes are available from all the major banks operating in Northern Ireland. This can be confusing for visitors as not only will you find standard English (Bank of England) notes in circulation but also but also Sterling from Ulster Bank, Bank of Ireland and Northern Bank as well as notes from Scottish banks and occasional Bank of Isle of Man notes.
All of these notes are accepted in general commerce throughout Northern Ireland. This can mean up to half a dozen different notes for the exact same denomination.
Important to note if traveling to England after your visit to Northern Ireland:
In England, most retailers will only accept standard Bank of England notes so remember to change any notes you have that were issued by a Northern Irish bank if travelling from Northern Ireland to England.