The current state of the knowledge of the size and the aggregation numbers of micelles formed in solutions of bile salts was evaluated. The experimental techniques considered include static light scattering, sedimentation equilibrium, membrane osmometry, sedimentation velocity and transla-tional diffusion. The theoretical background of each method is briefly discussed, the working equations are summarized, and the limitations of each technique are enumerated. Various interaction parameters and their effects on the measured micellar size are discussed. A brief survey of the recent experimental results from the author's laboratory is presented.