What's the Time?

Note: by "France", I mean continental (metropolitan) France.

Before 1891, every town and city in France had its own time based on local solar time - the time at which the sun is at its highest position in the sky. To align railway timetables, in 1891 time was unified in France and based on the solar time of Paris. In 1911 Metropolitan France adopted Greenwich Mean Time (GMT), which made sense as most of France falls geographically into the zone 7.5 degrees either side of the Greenwich Meridian. In 1923 Daylight Savings Time (DST) was introduced for the summer months.

In the summer of 1940, the German military authorities switched the occupied part of France to German summer time - GMT +2 - while Vichy France remained at GMT+1 (French summer time). The Vichy authorities kept GMT+1 (French summer time) during the winter of 1940–1941 and adopted GMT+2 (double summer time) in May 1941 in order to unify the railway timetables between occupied and Vichy France. After German occupation of the whole of France (1942) the whole of France used GMT+2 during the summer, and GMT+1 during the winter.

At the Liberation of France in the summer of 1944, Metropolitan France kept GMT+2 as it was the time then used by the Allies (British Double Summer Time). In the winter of 1944–1945 France switched to GMT+1, same as in the United Kingdom, and switched again to GMT+2 in April 1945 like its British ally. In September 1945, Metropolitan France returned to GMT+1. 

France was officially scheduled to return to GMT+0 on November 18, 1945, but the French government cancelled the decision in November 1945 and GMT+1 has since then remained the official time of Metropolitan France.

In 1976, daylight saving time was reintroduced in France for the first time since WW2 and since 1976 Metropolitan France has been at GMT+1 (now UTC+01:00) during the winter and GMT+2 (now UTC+02:00) during the summer. In 1996, daylight saving time was harmonized throughout the European Union which moved the end of DST to the last Sunday in October.

So, on Saturday night (or Sunday morning) don't forget to change your clocks.