  In many active stars the spots concentrate on two permanent active longitudes
which are 180 degrees apart. In some of these stars the dominant part of the
spot activity changes the longitude every few years. This so-called flip-flop
phenomenon has up to now been reported in 11 stars, both single and binary
alike, and including also the Sun. To explain this phenomenon, a
non-axisymmetric dynamo mode, giving rise to two permanent active longitudes at
opposite stellar hemispheres, is needed together with an oscillating
axisymmetric magnetic field. Here we discuss the observed characteristics of
the flip-flop phenomenon and present a dynamo solution to explain them.
