Future X-Ray Timing Missions

Thanks to the Rossi X-ray Timing Explorer (RXTE), it is now widelyrecognized that fast X-ray timing can be used to probe strong gravityfields around collapsed objects and constrain the equation of state ofdense matter in neutron stars. We first discuss some of theoutstanding issues which could be solved with an X-ray timing missionbuilding on the great successes of RXTE and providing an order ofmagnitude better sensitivity. Then we briefly describe the`Experiment for X-ray timing and Relativistic Astrophysics' (EXTRA)recently proposed to the European Space Agency as a follow-up to RXTEand the related US mission `Relativistic Astrophysics Explorer' (RAE).