  Today, the generation of magnetic fields in solar-type stars and its relation
to activity and rotation can coherently be explained, although it is certainly
not understood in its entirety. Rotation facilitates the generation of magnetic
flux that couples to the stellar wind, slowing down the star. There are still
many open questions, particularly at early phases (young age), and at very low
mass. It is vexing that rotational braking becomes inefficient at the threshold
to fully convective interiors, although no threshold in magnetic activity is
seen, and the generation of large scale magnetic fields is still possible for
fully convective stars. This article briefly outlines our current understanding
of the rotation-magnetic field relation.
