  The interplay of magnetic and semiconducting properties has been in the focus
since more than a half of the century. In this introductory article we briefly
review the key properties and functionalities of various magnetic semiconductor
families, including europium chalcogenides, chromium spinels, dilute magnetic
semiconductors, dilute ferromagnetic semiconductors and insulators, mentioning
also sources of non-uniformities in the magnetization distribution, accounting
for an apparent high Curie temperature ferromagnetism in many systems. Our
survey is carried out from today's perspective of ferromagnetic and
antiferromagnetic spintronics as well as of the emerging fields of magnetic
topological materials and atomically thin 2D layers.
