  The giant flares produced by highly magnetized neutron stars, "magnetars,"
are the brightest sources of high energy radiation outside our solar system.
Serendipitous observations with NASA's Rossi X-ray Timing Explorer (RXTE) of
the two most recent flares resulted in the discovery of high frequency
oscillations in their X-ray fluxes. The frequencies of these oscillations range
from about 20 Hz to as high as 1800 Hz, and may represent the first detection
of global oscillation modes of neutron stars. Here I will present an
observational and theoretical overview of these oscillations and discuss how
they might allow us to probe neutron star interiors and dense matter physics.
