This Fidabio ebook is a practical guide to measuring binding kinetics and molecular interactions in free solution, without surface immobilization or labelling. It explains how Flow Induced Dispersion Analysis (FIDA), on a Fida Neo instrument, measures binding affinity (KD) and association/dissociation rates by tracking changes in hydrodynamic radius, and shows real cases — including 50x faster affinity-reagent screening and binding kinetics measured directly in 100% plasma — where in-solution kinetics outperformed surface-based methods such as SPR and BLI. It is an example of using FIDA to measure binding affinity and kinetics under native, in-solution conditions.