The equations of the hydrodynamic theory of penetration of targets by shaped charge jets are presented first in general form. These equations are then expressed in the ideal form and examined by experimental observations. Then a nonideal theory is presented that takes into account heat losses by compression, shock heating, and radiated shock waves. The conditions for impact explosions of targets are then discussed and a theory extended to cover the entire velocity range of impact from the plastic deformation thresholdv&sgr;to well above the impact explosion thresholdvc. Some experimental evidence relating to this more general theory is also presented.