The Carnival (Karneval) is one the most celebrated events in Germany!
There are many cultural events happening throughout the year in Germany and in fact, it is the country with the most holiday days in the whole of Europe!
The carnival starts officially before Christmas, on the 11th of the 11th month at 11:11 am (elften elften elf uhr elf) with the offical meeting of the "Council of Eleven" (Elferrat), a German tradition dating from 1823.
The members of this council wear fool's caps as their official headgear. The council also organizes shows called Prunksitzung with club members and invited guests performing dance, comedy and songs, all dressed in costumes, of course!
But after that meeting, it stays more or less dormant until after Christmas, and in the case of most of German regions, until after the Three Kings, on January 6th.
It is a time of wild celebrations, and the western part of Germany especially (North Rhine-Westphalia and Rhineland-Palatinate), is famous for Karneval celebrations with parades and costume balls and hand-made costumes, and pranks of all sorts!
To this effect, there is a special day (Thursday before Ash Wednesday) for women called "Altweiber" (old women) or "Weiberfastnacht" (The women day) or also known in the regions of Baden-Württemberg, parts of Bavaria, and Alsace as Schmotziger Donnerstag or Fettdonnerstag. In standard German, schmutzig means "dirty", and one would think that schmotzig would mean the same, but actually the name is from the local dialect where schmotzig means "fat"; "Greasy Thursday" (similar to "Mardi Gras" (Fat Tuesday) in New Orleans).
During that day, Schmotziger Donnerstag, the ladies bring to work a pair of scissors and happily cut off the men ties! There are even stores selling specially ugly cheap ties for the occasion! It is also an excuse for the women to go out by themselves, for a girls only night, and leave the kids at home with their men.
In parts of East and South Germany (such as in Heidelberg) and Austria the carnival is called Fasching, while in Franconia and the southwest-parts of Germany it is called Fastnacht or Fasnet.
Although the German Karneval starts again after Christmas as early as the 6th of January with a few activities such as suppers, meeting with the queen and king, and balls, the actual carnival week with the real festivities starts on the Thursday before Ash Wednesday ("Aschermittwoch").
The parades are held mostly on the weekend before Rosenmontag (Rose Monday), or on the Monday itself before Shrove Tuesday.
In some areas, the parades are on Shrove Tuesday ("Faschingsdienstag") itself, but this is not the norm. Better ask around for the actual parade date of your region as it varies. Whenever is the parade, the carnival season, for the whole of Germany, finishes with Ash Wednesday, the main festivities happening around Rosenmontag. Traditionnally, the Karneval period is called the "Fifth Season of the year."