EU citizens working in Germany can bring their family, including spouses, children aged under 21, parents and grandparents, as long as they are financially secured and can provide enough living space. The right to bring along family members also applies to family members who are not citizens of an EU state. Family members do not require a work permit to take up employment.
For non-EU citizens with a (temporary or permanent) residence permit, family members normally include children under the age of 18, spouses and in some cases other family members. The family reunion (Familiennachzug) can only occur after certain conditions have been met, such as the size of the accommodation, the ability of the resident person to support dependents and a basic knowledge of German.
Some notes on marriages
Spouses have the right to come to Germany if the spouse already living in Germany has a valid residence permit (Aufenthaltserlaubnis). If the spouse living in Germany has a temporary or permanent residence permit (Aufenthaltserlaubnis), a spouse can only claim the right of Familiennachzug (family reunion) if the marriage took place before the person gained the residency and this was stated at the time of application. Both people have to be 18 years or older.
Residency rights are granted even if the partnership has ended, as long as the marriage was in place for two years after moving to Germany. If a couple divorced before two years has elapsed, individual residency rights are only granted in special cases.
Visits from friends and family
If friends or family members from abroad wish to visit you in Germany, this is not governed by the same regulations governing family members who wish to remain in Germany. Visitors need to get a visa before coming even if they only want to stay briefly in Germany. Since German diplomatic missions have a considerable amount of leeway when allocating visas, family ties are often taken into account and close relatives are often granted visas.
In order to gain a visa, your visitor must prove that s/he has means at their disposal to finance their stay in Germany. To prove this, you will generally need to sign a form at the local immigration office guaranteeing that you will cover the living costs of your visitor if necessary (Verpflichtungserklärung). The immigration office often charges a fee for processing this application.
For more information please check the website of the Federal Office for Migration and Refugees.