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Three types of variability have been associated with planetary nebula central stars (PNN). Short term variations (on timescales of minutes) have been attributed to non-radial pulsations in the atmospheres of hot, hydrogen-deficient central stars. Periodic variability over the course of $\sim 1$ day has been traced to binary PNN, in which the hemisphere of the main sequence companion is heated by the hot primary. But a third type of variability, which is irregular over timescales of several hours, has yet to be explained.
To investigate PNN variability, we have been monitoring planetary nebula central stars since 1986 using CCD cameras on the Kitt Peak and Cerro Tololo 0.9-m telescopes and the Cerro Tololo 1.5-m telescope. Our sample now consists of 112 objects, of which 90 have been searched for high frequency variations (periods less than $\sim 30$~min), 94 for changes of the order of several hours or more, and 57 for longer-term variability. We summarize our results and present representative light curves for all three classes of pulsating, binary, and irregular variables. We also test the hypothesis of Bond \& Ciardullo (1989, in White Dwarfs, I.A.U. Coll.~\#~114, p.~473), that irregular variability is associated with stellar winds by examining 5 nights of simultaneous optical photometry and IUE spectroscopy of the irregular variable, IC 418. Our data are examined for correlations between $y$ luminosity and the intensity of the stellar wind, as evidenced by IUE lines such as C~IV $\lambda 1549$ and Si~IV $\lambda 1397$. We find no obvious relationship between this object's stellar wind and its optical brightness.
