The German Naturalization

Reader German citizenship
Der Weg zur deutschen Einbürgerung (The way to German citizenship)

You can find more information about German law on citizenship and about naturalization for download here.

Nationality Act
date of issue 2009.10.22
Unofficial Translation by the Translation Division of the Federal Ministry of the Interior 2009/2011-wr
http://www.bmi.bund.de/SharedDocs/Gesetzestexte/EN/Staatsangehoerigkeitsgesetz_englisch.pdf?__blob=publicationFile