'Daylight Saving Time', DST for short, is a pretty new entry in the vocabulary of time-measurement.
Clock changes can be considered a symbol of a profound change in society, from predominantly rural to urban and industrialized.
The decision to adopt, observe or abolish Daylight Saving Time is taken by the government of a country, sometimes at short notice. In certain cases the rules are slightly adjusted, in others a major change is put forward to be debated and decided upon.
New rules for are still on the EU agenda, but no progress so far on the original proposal, to end clock changes. Read more about the the results of the public consultation
For the time being, all the countries in the European Union and a few others in Europe change their clocks on the same date and at the same time, according to EU Daylight Saving Time rules.
Note: as future changes are always possible, do let us know if we missed anything in what is never a stagnant world.
In the United States and Canada, a set of rules is also in operation, accompanied by some exceptions.
The United States, a multiple time-zone country, has seen some states trying to be exempted from the current rule. Florida is one example. You can have the picture in full on a comprehensive website, with news on the legislative process necessary to make any change possible.
In English, and in American English in particular, there is a phrase that makes it easier to remember when to put the clocks back or forward by one hour. "Spring forward, fall back".
The phrase is a pun and was coined on the basis of two seasons: spring and fall (autumn in UK). The verbal aid has been rendered a bit obsolete by digital clocks and devices. They should switch automatically between summer time and winter time.