First, it’s important to know exactly what the Blue Card is. The Blue Card is an approved EU-wide work permit allowing high-skilled non-EU citizens to work and live in any country within the European Union. In order to qualify for one of them you will need to have a degree, a employment contract with a German company and a minimum salary of €50,800 a year. However for those with skills in fields with labor shortages the minimum salary is €39,624 a year.
Once you are approved for a Blue Card, it will be valid for up to four years. It will depend on the length of your work contract, so for those contracts that are shorter than four years it will be valid for less.
After three years, those with blue cards are able to apply for an unlimited residence permit, which is called an Aufenthaltstitel. For those who have at least a B1 in German you are able to apply for an unlimited residence permit after just two years.