Multifit/Polydefix is an open source IDL software package for the efficient processing of diffraction data obtained in deformation apparatuses at synchrotron beamlines. Multifit allows users to decompose two-dimensional diffraction images into azimuthal slices, fit peak positions, shapes and intensities, and propagate the results to other azimuths and images. Polydefix is for analysis of deformation experiments. Starting from output files created in Multifit or other packages, it will extract elastic lattice strains, evaluate sample pressure and differential stress, and prepare input files for further texture analysis. The Multifit/Polydefix package is designed to make the tedious data analysis of synchrotron-based plasticity, rheology or other time-dependent experiments very straightforward and accessible to a wider community.