Flow Injection Analysis (FIA) is a continuous-flow analytical method that does not require complete physical mixing or chemical equilibrium, instead relying on the controlled dispersion of the injected sample within a carrier stream. This method allows for high sampling rates and the implementation of novel methodologies not feasible under batch conditions. FIA has evolved into three generations: FIA, Sequential Injection Analysis (SIA), and Lab-on-Valve (LOV). SIA uses a multiposition valve and syringe pump to aspirate and propel samples and reagents, minimizing waste and allowing for precise control over the mixing process. LOV further miniaturizes these systems, integrating all sample manipulations and detection into a monolithic structure, enabling the handling of bead materials and live cells. FIA's advantages include high sampling rates, minimal sample and reagent consumption, and the ability to exploit the interplay between kinetics and thermodynamics, making it suitable for a wide range of applications, including bioassays, process monitoring, and bioseparations. TheStopped-Flow approach, a powerful tool for determining analyte species in enzymatic or cellular assays, is particularly well-suited for process monitoring in bioreactors. LOV combined with bead injection (BI) has been used for cellular analyses and immunoassays, offering robust and precise methods for biomolecule quantification and separation.Flow Injection Analysis (FIA) is a continuous-flow analytical method that does not require complete physical mixing or chemical equilibrium, instead relying on the controlled dispersion of the injected sample within a carrier stream. This method allows for high sampling rates and the implementation of novel methodologies not feasible under batch conditions. FIA has evolved into three generations: FIA, Sequential Injection Analysis (SIA), and Lab-on-Valve (LOV). SIA uses a multiposition valve and syringe pump to aspirate and propel samples and reagents, minimizing waste and allowing for precise control over the mixing process. LOV further miniaturizes these systems, integrating all sample manipulations and detection into a monolithic structure, enabling the handling of bead materials and live cells. FIA's advantages include high sampling rates, minimal sample and reagent consumption, and the ability to exploit the interplay between kinetics and thermodynamics, making it suitable for a wide range of applications, including bioassays, process monitoring, and bioseparations. TheStopped-Flow approach, a powerful tool for determining analyte species in enzymatic or cellular assays, is particularly well-suited for process monitoring in bioreactors. LOV combined with bead injection (BI) has been used for cellular analyses and immunoassays, offering robust and precise methods for biomolecule quantification and separation.