  We provide an overview of stellar variability in the first quarter of data
from the Kepler mission. The intent of this paper is to examine the entire
sample of over 150,000 target stars for periodic behavior in their lightcurves,
and relate this to stellar characteristics. These data constitute an
unprecedented study of stellar variability given its great precision and
complete time coverage (with a half hour cadence). Because the full Kepler
pipeline is not currently suitable for a study of stellar variability of this
sort, we describe our procedures for treating the "raw" pipeline data. About
half of the total sample exhibits convincing periodic variability up to two
weeks, with amplitudes ranging from differential intensity changes less than
10^{-4} up to more than 10 percent. K and M dwarfs have a greater fraction of
period behavior than G dwarfs. The giants in the sample have distinctive
quasi-periodic behavior, but are not periodic in the way we define it. Not all
periodicities are due to rotation, and the most significant period is not
necessarily the rotation period. We discuss properties of the lightcurves, and
in particular look at a sample of very clearly periodic G dwarfs. It is clear
that a large number of them do vary because of rotation and starspots, but it
will take further analysis to fully exploit this.
