The Central European Summer Time (CEST) begins on the last Sunday in March, at 2 o'clock Central European Time. On this day at 2 o'clock, clocks will be set forward one hour, to 3 o'clock. The better use of daylight hours has been the aim of the introduction of Summer Time (also called Daylight Savings Time).
The Central European Summer Time (CEST) always ends on the last Sunday in October, at 3 o'clock Central European Summer Time. On this day, the time will be rolled back one hour, from 3 o'clock to 2 o'clock. This hour therefore appears twice, and for identification purposes the first one is referred to as 2A and the second one as 2B.
Further information:
On the pages of the working group "Unit of Time" you find detailed information about the summer time in Germany.