People are being reminded that the clocks go back at 2.00am on Sunday.
This marks the beginning of 'Winter Time', where clocks and watches should be put back one hour to 1:00am Greenwich Mean Time (GMT).
Winter time will end on Sunday March 29th 2020.
Earlier this year, MEPs voted to end the practice of adjusting clocks twice a year from 2021.
The proposal for change followed a major public consultation in 2018, which received 4.6 million responses from all 28 member states.
Of these, 84% were in favour of discontinuing the biannual clock changes - while 16% wanted to keep them.
While 88% of Irish people who took part in the survey wanted the change abolished - with only 12% suggesting it should stay.
However, the Irish Government said it intends to fight the change.
In July, Justice Minister Charlie Flanagan said it could lead to two time zones on the island of Ireland when the UK leaves the EU.
Minister Flanagan was also concerned that altering how countries change the clocks could lead to a patchwork of different time zones across the EU, instead of having geographical zones as is done now.
Currently, clocks are changed twice per year in order to cater for the changing patterns of daylight and to take advantage of the available daylight in a given period.
EU countries switch to summer time on the last Sunday of March and back to standard time on the last Sunday of October.