Rearrangements & Softness in Disordered Solids aims to develop fundamental understanding of the organization and proliferation of localized particle-scale rearrangements in disordered solids deformed just beyond the onset of yield, and thereby identify strategies for controlling nonlinear mechanical response and enhancing toughness. The materials studied by the team span a wide range of length scales from amorphous carbon and atomic/molecular glasses, to nanoparticles and colloids, to macroscopic bubbles and grains. When pushed beyond yield, some materials crack or shatter due to rearrangements that collect along planes, whereas others flow smoothly because rearrangement events remain separated. New theoretical concepts, some based on machine learning, will be developed to understand this dramatic difference, and these theories will be tested by atomistic simulations and experiments on systems for which it is possible to measure microstructure versus time during a large imposed deformation. Ultimately, these factors will be optimized to widen the window between yield and failure and hence to improve toughness.