Analytical ultracentrifugation is a classical method of biochemistry and mo
lecular biology. Because it is a primary technique, sedimentation can provi
de first-principle hydrodynamic and first-principle thermodynamic informati
on for nearly any molecule, in a wide range of solvents and over a wide ran
ge of solute concentrations. For many questions, it is the technique of cho
ice. This review stresses what information is available from analytical ult
racentrifugation and how that information is being extracted and used in co
ntemporary applications.