A meso-scale model for conventional concrete as a composite with three components of materials, that is, aggregates, mortar matrix and an interfacial transition zone was utilized to simulate the compressive failure of concrete. Being a meso-scale model, it simulates the interaction between particles along failure planes such as that studied in the established theories of shear-friction or aggregate interlock. The meso-scale model was used to study the softening of concrete by analyzing tests on eccentrically loaded prisms and confined concrete prisms. It was found to accurately predict crack patterns and deformations in specimens as well as both the axial and lateral stress-strain relationships and, furthermore, explained the mechanics behind the effects of confinement, size and shape. It is suggested that this research shows that the softening of concrete is not a material property but a mechanism and that the meso-scale model is ideally suited for studying and quantifying this important behaviour.