Summer time in Europe in the context of European Union Directive

Daylight saving time (DST), also referred to as daylight savings time, daylight time (United States and Canada), or summer time (United Kingdom, European Union, and others), is the practice of advancing clocks to make better use of the longer daylight available during summer so that darkness falls at a later clock time. The standard implementation of DST is to set clocks forward by one hour in spring or late winter, and to set clocks back by one hour to standard time in the autumn (or fall in North American English, hence the mnemonic: "spring forward and fall back").

In several countries, the number of weeks when DST is observed is much longer than the number devoted to standard time.

Europe spans seven primary time zones (from UTC−01:00 to UTC+05:00), excluding summer time offsets (five of them can be seen on the map, with one further-western zone containing the Azores, and one further-eastern zone spanning the Ural regions of Russia and European part of Kazakhstan). Most European countries use summer time and harmonise their summer time adjustments; see Summer time in Europe for details.

The time zones actually in use in Europe differ significantly from uniform zoning based purely on longitude, as used for example under the nautical time system. The world could in theory be divided into 24 time zones, each spanning 15 degrees of longitude. However, due to geographical and cultural factors, it is not practical to divide the world so evenly, and actual time zones may differ significantly from those based purely on longitude. In Europe, the widespread use of Central European Time (CET) causes major variations in some areas from solar time. Based on solar time, CET would range from 7.5 to 22.5°E. However, for example Spain (almost entirely in the Western hemisphere) and France (almost entirely west of 7.5°E, as illustrated in the map below) should theoretically use UTC, as they did before the Second World War. The general result is a solar noon which is much later than clock noon, and later sunrises and sunsets than should theoretically happen. The Benelux countries should also theoretically use GMT.