The author briefly reviews the factors important to the blowcount (N) values obtained from the standard penetration test (SPT), and describes the dynamics of the SPT in terms of wave transmission theory and measurements. The SPT appears to correlate well qualitatively with sand liquefaction potential, with N proportional to the factor of safety against liquefaction. The SPT can also provide the basis for the field-model determination of the J_s, and J_p damping coefficients in the wave equation analysis of pile-driving problems. An example indicates it may also correlate locally with shear wave velocity in sands. Because of its current variability, however, the profession needs an improved, possibly alternative ASTM standard before we use the SPT in important dynamic design problems. The author suggests using a mechanized hammer drop system producing a fixed energy content in the first compression wave in the rods, and the use of rotary drilling with the hole filled with drilling mud at all times.