This book provides simple physical models to represent the unbounded soil in time and frequency domain analysis. They do not supplant the more generally applicable rigorous methods, but rather supplement them. The physical models used consists of the following representations: cones based one-dimensional rod theory; lumped-parameter models with frequency-independent springs, dashpots, and masses; and prescribed wave patterns in the horizontal plane. The physical models thus offer a strength-of-materials approach to foundation dynamics.