  The Surface Brightness Fluctuation (SBF) method is a powerful tool for
determining distances to early-type galaxies. The method measures the intrinsic
variance in a galaxy's surface brightness distribution to determine its
distance with an accuracy of about 5%. Here, we discuss the mathematical
formalism behind the SBF technique, its calibration, and the practicalities of
how measurements are performed. We review the various sources of uncertainties
that affect the method and discuss how they can be minimized or controlled
through careful observations and data analysis. The SBF technique has already
been successfully applied to a large number of galaxies and used for deriving
accurate constraints on the Hubble-Lema\^itre constant $H_0$. An approved JWST
program will greatly reduce the systematic uncertainties by establishing a firm
zero-point calibration using tip of the red giant branch (TRGB) distances. We
summarize the existing results and discuss the excellent potential of the SBF
method for improving the current constraints on $H_0$.
