Gravitational radiation can drive a fluid instability in a rotating neutron star, causing it to spin down to slower rotation rates. This instability has been understood for the last quarter of a century. However, until recently is was never clear that the process would operate in astrophysical circumstances. The surprising discovery, due to Nils Andersson, that sluggish “ocean” currents (known to astronomers asr-modes) can be unstable at arbitrarily slow rotation rates has opened the door to a number of interesting applications in relativistic astrophysics. One exciting implication is that the instability may explain the spin rate of pulsars born with high angular velocity. It also may be possible to observe the gravitational radiation associated with these currents with an advanced version of LIGO. ©1999 American Institute of Physics.