The tolerance to ballistic impact of graphite/epoxy and boron/epoxy composites has been investigated. The effects of preload, of ply layups, and of projectile velocity have been examined for 30 caliber armor-piercing projectiles striking the plate at a 0 deg obliquity. A limited number of tests were performed on glass/epoxy laminates and on type 6061-T6 aluminum panels. Several tests were conducted using 50 caliber armor-piercing projectiles. High-speed photography was used to determine the overall ballistic response, as an additional check on projectile velocity, and to determine when crack initiation occurred. The fracture toughness of each type of laminate was determined and both the residual strength (the nominal stress to which a panel which did not fail during performation can be loaded) and the threshold strength (the lowest pre-impact stress which results in failure upon impact) are shown to correlate directly with the toughness.