People all over the world have been toasting what is described as a momentous anniversary for the Guinness company.
250 years ago Arthur Guinness signed a 9,000 year lease on the St James's Gate brewery in Dublin.
And the first toast to mark the anniversary took place this evening at 17.59.
Thousands across the country followed suit and many more across the world raised a glass.
As part of the celebrations, willing performers came from near and far to play surprise gigs at venues throughout Dublin, while thousands attended an invitation-only party at the Guinness Storehouse.
An Post has printed a commemorative stamp in honour of Arthur Guinness, as was done for the 200th anniversary in 1959.
And with an online petition to make Arthur's Day a national holiday, Guinness may find that 250 years until the next big celebration is just too long to wait.