The application of seismic methods for rock and soil-mass characterization has proved to be useful for engineering projects of any kind. These methods can predict the presence and geometry of low-competent subsoil materials and can define preliminary structural designs for each project. In three studies in Colombia, refraction tomography and multichannel analysis of surface waves (MASW) were applied for road tunnels and multistory building construction, respectively. In situ rock and soil types were classified based on P- and S-wave measurements, and preliminary structural designs and construction methods were recommended for each case. Both rock and soil classifications and preliminary structural designs must be refined with direct subsoil-characterization methods such as core drilling and laboratory testing.