  I review theoretical treatments of diffusion in crowded (i.~e., non-dilute)
solutions of globular macromolecules. The focus is on the classical
statistico-mechanical literature, much of which dates to before 1990. Classes
of theoretical models include continuum treatments, correlation function
descriptions, generalized Langevin equation descriptions, Smoluchowski and
Mori-Zwanzig descriptions, and a brief but encouraging comparison with
experimental results. The primary emphasis is on measurements made with
quasi-elastic light scattering spectroscopy; I also discuss outcomes from
fluorescence photobleaching recovery, fluorescence correlation spectroscopy,
pulsed-gradient spin-echo nuclear magnetic resonance, and raster image
correlation spectroscopy. I close with a list of theoretical papers on the
general topic.
