Abstract This paper describes an adaptation of the Optimally Localized Averaging (OLA) inversion technique, originally developed for geo- and helioseismological applications, to the interpretation of solar spectroscopic data. It focuses on inverting the thermodynamical properties of the solar atmosphere, assuming that the atmosphere and radiation field are in local thermodynamic equilibrium (LTE). We leave inversions of magnetic field and non-LTE inversions for future work. The advantage with the OLA method is tha…