  We examine the use of surface brightness fluctuations (SBF) for both stellar
population and distance studies. New V-band SBF data are reported for five
Fornax cluster galaxies and combined with literature data to define a new
V-band SBF distance indicator. We use new stellar population models, based on
the latest Padua isochrones transformed empirically to the observational plane,
to predict SBF magnitudes and integrated colours for a wide range of population
ages and metallicities. We examine the sensitivity of the predictions to
changes in the isochrones, transformations, and IMF. The new models reproduce
the SBF data for globular clusters fairly well, especially if higher
metallicity globulars are younger. The models also give a good match to the
"fluctuation colors" of elliptical galaxies. In order to obtain theoretical
calibrations of the SBF distance indicators, we combine our single-burst models
into composite population models. These models reproduce the observed behavior
of the SBF magnitudes as a function of stellar population parameters, including
the steep colour dependence found for HST/WFPC2 F814W SBF data. Because the
theoretical SBF calibrations are fairly sensitive to uncertain details of
stellar evolution, the empirical calibrations are more secure. However, the
sensitivity of SBF to these finer details potentially makes it a powerful
constraint for stellar evolution and population synthesis. [abbridged]
