  We analyze the properties of quasar variability using repeated SDSS imaging
data in five UV-to-far red photometric bands, accurate to 0.02 mag, for 13,000
spectroscopically confirmed quasars. The observed time lags span the range from
3 hours to over 3 years, and constrain the quasar variability for rest-frame
time lags of up to two years, and at rest-frame wavelengths from 1000 Ang. to
6000 Ang. We demonstrate that 66,000 SDSS measurements of magnitude differences
can be described within the measurement noise by a simple function of only
three free parameters. The addition of POSS data constrains the long-term
behavior of quasar variability and provides evidence for a turn-over in the
structure function. This turn-over indicates that the characteristic time scale
for optical variability of quasars is of the order 1 year.
