The genitive case
This case is used when you want to express a possession or belonging of a person or an object to another person or object. In English, the preposition of or the apostrophe are indicators for this type of object. Also, some prepositions, such as wegen (because of) or trotz (despite) are followed by a noun in the genitive case.
Die Tante meiner Mutter ist unausstehlich.
Die Tür meines Autos ist kaputt.
The door of my car is broken.
Wegen des Regens sind die Straßen geschlossen.
Because of the rain the roads are closed.
Trotz des schlechten Wetters waren viele Touristen am Strand.
Many tourists were at the beach despite the bad weather.
All in all, the genitive case is less frequently used than its big brothers accusative and dative. In spoken, and more and more in written German as well, it is nowadays often replaced by a dative object using the preposition von.
Die Frau meines Bruders ist wirklich nett. = Die Frau von meinem Bruder ist wirklich nett.
My brothers wife is really nice = The wife of my brother is really nice.
Der Schlüssel meiner Wohnung ist unter der Mutter = Der Schlüssel von meiner Wohnung ist unter der Matte.
My apartments key is under the doormat. = The key of my apartment is under the door mat.
By the way, the letter s at the end of an article is quite characteristic for this case as you can see here.
Table: Articles in the genitive case
Masculine feminine Neuter Plural
Definite article des der des der
Indefinite article eines einer eines -
Genitive

(deleted)
May 27, 2008