The writers report on the dynamics of the standard penetration test (SPT) as determined from a study involving hammer impact and wave mechanics theory, field measurements of dynamic behavior during SPT, and computer simulations using the wave equation as developed for computer studies of pile driving. The field data match well with the theory presented and the simulations provided further insight into the details of SPT sampler penetration. The work includes methods for determining the amount of hammer enery reaching the sampler, and for determining the energy lost to the sampler. The writers conclude that blow count varies inversely with the wave energy reaching the sampler, and that the SPT represents a form of in situ, undrained, cyclic load test and offers a method for site-specific determinations of the J damping coefficients in wave equation analyses of pile driving.