What about family?

Securing the livelihood.

Spouses and underage kids (minors) may come along.
However, the salary/earnings of the applicant must be sufficient to secure the family's liveli-hood.

The actual costs of living must be estimated, for every adult additionally 357 Euros and for kids, depending on age, amounts between 251 and 287 Euros (2012 figures). This should not present a problem for a qualified employee.
Health insurance for the entire family exists via the income earner.

The apartment must be large enough. For every family member 12 square meters are re-quired. Thus 48 square meters are necessary for a family of four.
The husband or spouse can normally begin to work immediately.
He or she must have completed a German course in the home country, however language level A1 is sufficient. (very simple conversations in every day situations)

With a visa according to § 19a AufenthG (blue card), this is no longer a requirement.

Kids.
Kids up to the age of 18 may come along.
For children aged 16 years or above, however, good language skills (language level C1) are expected or "positive integration prognosis" is required, which of course requires some knowledge of German. A preparatory German course in your home country is thus very use-ful.
Public education and the university in Germany are largely free of charge.

Children above the age of 18 have no legal right to enter with their family. However if they want to study at the university or do a two-three year vocational training in Germany, this is usually possible.