'Daylight Saving Time', DST for short, is a pretty new acquisition 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.
A little more than a hundred years old, DST (read the story here ) is not a universal norm though.
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, as is the case of EU Summer Time. (The results of the public consultation and the proposed timetable here )
For the time being, all the countries in the European Union (EU) and a few others in Europe change their clocks on the same date and at the same time, according to EU current Summer 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, there is as well a set of rules, accompanied by some exceptions.
USA, 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.