'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 )
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.
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.
In the United States and Canada, there is as well a set of rules, accompanied by some exceptions.
Note: as future changes are always possible, do let us know if we missed anything in what is never a stagnant world.
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.