Internal elastic strains and textures are measured using monochromatic x-ray diffraction in -Fe plastically deformed up to 17.5 GPa and 600 K in the deformation-DIA. We observe the development of a strong 0 0 0 1 compression texture along with a strongly non-linear behavior of 0 0 0 2 lattice strains. We then use an elastoplastic self-consistent polycrystal model to simulate the macroscopic flow curves, internal strain and texture development within the sample. Input parameters are single-crystal elastic moduli, critical resolved shear stresses, and hardening behavior of the slip and twinning mechanisms. The model is found to reproduce the experiment data with basal slip as the easiest and most active deformation mechanism. Other active mechanisms are tensile twinning, prismatic and pyramidal 〈c + a〉 slip. Tensile twinning is most active at lower temperatures (e.g. 400 K) and a higher strain rate. In most cases, the twinning activity occurs early in the deformation and later saturates. It is also responsible for the non-linear behavior of 0 0 0 2 lattice strains. Later in the deformation, the plastic activity of -Fe is controlled by basal, prismatic and pyramidal 〈c + a〉 slip.