Starting from this chapter, our primary focus will be on solving seismic wave problems in two simplified medium models: an isotropic homogeneous infinite medium and an isotropic homogeneous semi-infinite medium. The main topic of this book, the Lamb’s problem, pertains to the latter. However, the infinite medium is the only scenario in elastodynamics where simple closed-form solutions exist, serving as the foundation for further consideration of the semi-infinite medium problem. In this chapter, we will first address seismic wave issues within this simple model, with a focus on Green’s functions in infinite space and the displacement field caused by a dislocation source.