Over the last decade considerable evidence has been found for the
existence of magnetars, neutron stars whose electromagnetic emission
is powered by the decay of their extremely high magnetic field.
Two classes of high-energy sources have been identified with slowly
spinning magnetars. A new perspective in this
field was brought about by the 2004 December 27 giant flare from
SGR 1806-20. The enormous energy liberated in this event
points to an internal magnetic field strength of >10^16 Gauss.
I will survey the implications of this extroardinary event
for: (a) developing the field of neutron star astroseismology;
(b) giving rise to exceptionally high luminosity derivatives
from a non-expanding source; (c) detecting gravitational wave signals
from newborn magnetars. Prospects for the future will also be outlined.