Recent advances in high-resolution spectropolarimetric instrumentation—enabled by facilities such as the Goode Solar Telescope, Daniel K. Inouye Solar Telescope, Solar Orbiter, and IRIS—allow coordinated observations in multiple chromospheric spectral lines (e.g., Ca II, Hα, Mg II, He I 10830 Å). Combined with state-of-the-art non-LTE inversion techniques and high-performance computing, these developments provide increasingly robust constraints on the thermodynamic and magnetic structure of the solar chromosphere. Significant progress has been made in inferring key parameters, including vector magnetic fields, plasma velocities, temperature stratification, and density, across diverse solar environments from quiet Sun to flaring regions. Advances in radiative MHD simulations, forward modeling, and synthetic diagnostics further support interpretation and validation of these measurements. This session invites contributions on multi-line spectropolarimetry, non-LTE inversions, and model–data integration, and will assess current challenges and future needs in chromospheric diagnostics, instrumentation, and analysis frameworks.