Summer time in Europe

European Summer Time is the variation of standard clock time that is applied in most European countries, not including Iceland, Belarus, Turkey and Russia — in the period between spring and autumn, during which clocks are advanced by one hour from the time observed in the rest of the year, in order to make the most efficient use of seasonal daylight. It corresponds to the notion and practice of "daylight saving time" to be found in many other parts of the world.

European Summer Time is observed across three time zones, beginning at 01:00 UTC/WET (02:00 CET, 03:00 EET) on the last Sunday in March and ending at 01:00 UTC (02:00 WEST, 03:00 CEST, 04:00 EEST) on the last Sunday in October each year. This means that Summer Time lasts, depending upon the calendar year, for either 30 or 31 weeks of the year.

Summer Time was first introduced during the First World War. However, most countries discontinued the practice after the war. It was then restarted in various countries during the Second World War and its immediate aftermath. Again it was widely cancelled by the 1950s, although re-introduced in isolated cases until the late 1960s when the energy crisis began to prompt policy makers to re-introduce the policy across the continent. It has remained in place in most European countries since that time.

Historically the countries of Europe had different practices for observing Summer Time, but this hindered coordination of transport, communications and movements. Starting in 1981 the European Community began issuing directives requiring member states to legislate particular start and end dates for Summer Time.

Since 1981 each directive has specified a transition time of 01:00 UTC and a start date of the last Sunday in March, but the end dates have differed. Successive Directives laid down two dates for the end: one on the last Sunday in September applied by the continental Member States, and the other on the fourth Sunday in October for the United Kingdom and Ireland. In 1996 the end date was changed to the fourth Sunday in October for all countries. In 1998 the end date was adjusted to be the last Sunday in October; this happened to be the same as the previous rule for 1996 and 1997. The ninth directive, currently in force, has made this permanent.

...
Wikipedia