  Recent surveys have discovered hundreds of low surface brightness galaxies,
systems with central surface brightness fainter than 22.0 B mag arcsec^-2, in
the local universe. Plots of the surface brightness distribution - that is, the
space density of galaxies plotted against central surface brightness - show a
flat space density distribution from the canonical Freeman value of 21.65
through the current observational limit of 25.0 B mag arcsec^-2. It is
therefore extremely important to understand these diffuse systems if we wish to
understand galaxy formation and evolution as a whole. This talk is a review of
both the known properties of low surface brightness galaxies and of popular
theories describing the formation and evolution of these enigmatic systems.
