  In this paper we first discuss observational evidence of longitudinal
concentrations of magnetic activity in the Sun and rapidly rotating late-type
stars with outer convective envelopes. Scenarios arising from the idea of
rotationally influenced anisotropic convective turbulence being the key
physical process generating these structures are then presented and discussed -
such effects include the turbulent dynamo mechanism, negative effective
magnetic pressure instability (NEMPI) and hydrodynamical vortex instability.
Finally, we discuss non-axisymmetric stellar mean-field dynamo models, the
results obtained with them, and compare those with the observational
information gathered up so far. We also present results from a pure
alpha-squared mean-field dynamo model, which show that time-dependent behavior
of the dynamo solutions can occur both in the form of an azimuthal dynamo wave
and/or oscillatory behavior related to the alternating energy levels of the
active longitudes.
