  We present results from a monitoring program of 42 quasars from the Palomar
Green sample. The objects were observed for 7 years at the Wise Observatory, as
part of a long term effort to monitor AGN of various types. This is the most
extensive program of its kind carried out to date on a well-defined optically
selected quasar sample. The typical sampling interval is ~40 days. One third of
the quasars were observed at ~60 epochs and the rest at ~30 epochs in two bands
(B&R) with photometric accuracy of ~0.01 mag. We present lightcurves for all of
the sources and discuss the sample variability properties. All of the quasars
in the sample varied during the campaign with intrinsic rms amplitudes of
5%<sigma_B<34% and 4%<sigma_R<26%. The rms amplitude and colour for the entire
sample are sigma_B=14%, sigma_R=12%, and sigma_{B-R}=5%. On time scales of 100-
1000 days the power spectra of the sources have a power-law shape with index
approximately 2.0 and a spread <0.6. At least half of the quasars, particularly
those that are most variable, become bluer when they brighten, and the rest do
not show this behaviour. We quantify this phenomenon, which has been observed
previously mainly in Seyfert galaxies. The quasars which are most variable tend
also to exhibit asymmetry in their variations, in the sense that the
brightening phases last longer than the fading phases. We have searched for
correlations between the measured variability properties and other parameters
of the quasars, such as luminosity, redshift, radio loudness, and X-ray slope.
We find several new correlations, and reproduce some of the correlations
reported by previous studies.
