During the last decades we have assisted at a considerable shift from laboratory testing to in situ testing to the point that, today, in situ testing often represent the major part of a geotechnical investigation. Recommendations given in the State of the Art at the last Geotechnical World Conference in 2009 and in the Mitchell Lecture at the last International Conference on Geotechnical and Geophysical Site Characterization in 2012 indicate that direct-push in situ tests, such as the Seismic Cone Penetration Test (SCPT) and the Seismic Dilatometer Test (SDMT), are fast and very convenient tests for routine site investigations. The aim of this paper is to describe the SDMT, the obtained information and some engineering applications for design infrastructures: settlements for bridges, subgrade compaction control for roads and liquefaction for harbors.