Regardless of nationality, any foreigner who wishes to live and work in Germany requires a residency permit (Aufaenhalt). These can either be applied for in person at a German embassy or consulate, or through the immigration authorities in Germany.
There are three different types of residence permits for Germany.
The Temporary Residence Permit or Limited Residence Permit (Aufenthaltserlaubnis) is for shorter stays of up to one year. However, it has the possibility of extension provided that your situation does not change and that you fulfil the requirements. It is granted to foreign nationals if they have a specific reason for staying in Germany. However, you cannot engage in an activity that your residence permit doesn’t allow. If your temporary residence permit is for studying, you can’t work, and vice versa.
The EU Blue Card is similar to the Temporary Residence Permit, but is only accessible by certain expats and has longer validity. The EU Blue Card is for foreign nationals of non-EU countries who are highly skilled in a profession and want to work in Germany. Those who are more likely to get the EU Blue Card have an IT or STEM (Science, Technology, Engineering, Mathematics) background. They must obtain a job offer in Germany in the same field as their educational qualification, they should earn above a certain income bracket, and they should have a high level of German proficiency.
Lastly, the Permanent Residence Permit (Niederlassungserlaubnis) allows expats to live and work in Germany and travel in and out of the country whenever required. Usually, only expats who have held a Temporary Residence Permit for a few years or those with the EU Blue Card can get this permit. They need to prove that they have worked for at least five years, that the Federal Employment Agency approved their job, and that they have paid the necessary taxes and contributions to the government. Additionally, the German language proficiency requirements are more stringent, so you will need to know more advanced German. If expats have a permanent residence permit, their children and spouse are allowed to join them.