The settlement permit is valid for an unlimited period of time. This enables you to work in Germany.
Generally you have to hold a residence permit for five years and fulfil other conditions to obtain a settlement permit.
Anyone wanting to apply for a settlement permit must independently ensure that they and their family members have the means of subsistence, have adequate knowledge of German and must not have criminal record. Under certain circumstances, a residence permit may be issued without any time limits, for example, for highly qualified immigrants.