To gain fundamental understanding of energy absorbing mechanisms during high velocity impact of plain weave S-2 glass/epoxy composites, single layer composites are ballistically tested and modeled. Targets were 0.6 m by 0.6 m with free boundaries. Targets were perforated by 17 grain fragment simulating projectiles. Experiments focused on determining ballistic limit velocity and associated damage modes. Experiments were simulated with a continuum finite element model with effective plain weave properties that predicted the ballistic limit velocity with 6% error. A mesoscale model incorporating the woven fabric architecture and lower length scale energy absorbing mechanisms was also developed. The mesoscale model includes accurate geometry and fiber volume fraction, rate-dependent matrix behavior, and important damage mechanisms including tow-tow delamination, tow pullout and frictional sliding. The mesoscale model predicted ballistic limit velocity with 1% error and more accurately predicts the deformation modes during ballistic impact and penetration than the continuum modeling approach. The mesoscale model indicated two phases of penetration, the first dominated by momentum transfer and the second dominated by tow tension and pullout. In a materials-by-design framework, the mesoscale model was used to quantify energy dissipation and identify important damage mechanisms that could be optimized to provide improved ballistic penetration resistance.