This peer-reviewed book chapter (in Clinical Applications of Capillary Electrophoresis: Methods and Protocols) is a hands-on protocol for Flow Induced Dispersion Analysis (FIDA), an in-solution method for quantifying and characterizing proteins under native conditions. FIDA measures the apparent hydrodynamic radius of a fluorescent indicator using Taylor Dispersion Analysis in a thin fused-silica capillary: the unbound indicator is small, and its apparent size increases as it binds the target, so the change reports on the interaction. Titrating the analyte produces a binding curve yielding the dissociation constant (Kd) and a standard curve for determining analyte concentration in unknowns such as plasma or serum. As a surface-free assay it shares goals with ELISA, SPR and BLI while avoiding immobilization. The chapter details the full workflow — instrumentation, buffer and indicator preparation, uncoated vs PEG-coated capillaries, mixing modes, Taylorgram analysis and Kd/concentration calculation.