Among other basic requirements, you must fulfill the following criteria in order to receive a residence permit:

• You entered the country with the required visa and provided the information necessary for acquiring a residence permit (regarding the purpose of your stay in particular) during the visa application process.
• Your identity has been established and you meet the relevant passport requirements.
• You can support yourself without public welfare assistance (except for in exceptional cases, this is based on your ability to secure income that at least covers the simple standard rate of social assistance, the cost of housing and heating, and any health insurance contributions).
• There is no outstanding reason for which you could be deported.
• If you are not otherwise entitled to a residence permit, your stay nevertheless presents no hindrance or danger to the interests of the Federal Republic of Germany for any other reason.

Further criteria may be required based on the purpose for which you are seeking a residence permit.

If you are a foreign citizen who possesses long-term legal residency in another EU member-state (meaning you hold a national residence title that grants "permanent residency in the European Community" in that state's official language), you can usually obtain a residence permit for Germany if you plan to stay here for longer than three months. This permit will also allow you to work, provided that the applicable regulations concerning your intention to seek employment or vocational training in Germany are met. A residence permit can also be revoked in these cases, such as if your status as a long-term legal resident of another EU member-state becomes invalid. 

A permanent residence permit is an open-ended residence permit that authorizes you to work and move freely throughout the country. If you initially receive a temporary residence permit, you will generally be eligible for permanent residency after a certain amount of time passes. 
To obtain a permanent residence permit, you must apply in writing at the foreign citizens' office of your main place of residence. 

Who can apply for a permanent residence permit?

The requirements for acquiring permanent residency are as follows:

• Your identity has been established and you meet the applicable passport requirements. Here, having a substitute form of identification is also sufficient.
• You can support yourself without relying on public welfare assistance.
• There is no outstanding reason for which you could be deported.
• You do not have a criminal record.
• Your stay presents no hindrance or danger to the interests of the Federal Republic of Germany.
• You have been in possession of a residence permit for at least five years.
• Other time requirements may apply depending on the purpose for which you received your current residence permit.
• You have paid into the statutory retirement insurance fund or another insurance institution providing comparable services for a total of five years.
• You are allowed to work and hold all of the permits your occupation requires.
• You have adequate German language skills and basic knowledge of Germany's laws and social structures.
• You have sufficient living space for yourself and your family.