  We report on long-term monitoring of anomalous X-ray pulsars (AXPs) using the
Rossi X-ray Timing Explorer. Using phase-coherent timing, we find a wide
variety of behaviors among the sources, ranging from high stability (in 1E
2259.1+586 and 4U 0142+61), to instabilities so severe that phase-coherent
timing is not possible (in 1E 1048.1-5937). We note a correlation in which
timing stability in AXPs decreases with increasing spin-down rate. The timing
stability of soft gamma repeaters in quiescence is consistent with this trend,
which is similar to one seen in radio pulsars. We consider high signal-to-noise
ratio average pulse profiles as a function of energy for each AXP, and find a
variety of behaviors. We find no large variability in pulse morphology nor in
pulsed flux as a function of time.
