  The magnetic activity levels of planet host stars may differ from that of
stars not known to host planets in several ways. Hot Jupiters may induce
activity in their hosts through magnetic interactions, or through tidal
interactions by affecting their host's rotation or convection. Measurements of
photospheric, chromospheric, or coronal activity might then be abnormally high
or low compared to control stars that do not host hot Jupiters, or might be
modulated at the planet's orbital period. Such detections are complicated by
the small amplitude of the expected signal, by the fact that the signals may be
transient, and by the difficulty of constructing control samples due to
exoplanet detection biases and the uncertainty of field star ages. We review
these issues, and discuss avenues for future progress in the field.
