This paper presents a summary of some recent experimental work aimed at evaluating the role of various physical parameters in high-speed impact phenomena. It is shown that penetration into thick targets by projectiles of the same material, for certain common metals, can be expressed approximately through a single relationship of the form (p/d) = 2.5(V/c)1.4 in a range of about 0.1 ≤ (V/c) ≤ 1.0. Here p represents penetration (crater depth) measured from the initial target surface, d a characteristic dimension of the projectile, and V the impact velocity. c is the “sonic” velocity in the projectile and target material as expressed by the formula , where E is Young’s modulus and ρ the density. Experimental results are given for steel, aluminum, brass, lead, magnesium, and a magnesium-lithium alloy.