The seismic dilatometer (SDMT) is a combination of the standard DMT with a seismic module for measurement of the shear wave velocity Vs. This paper summarizes the experience gained from a large number of tests performed with the SDMT at several sites in the recent years and illustrates the main lessons learned from the use of the tool. In particular, the paper presents an overview of the SDMT equipment and test layout, comparisons of Vs measured by SDMT and by other methods and a selection of significant SDMT results and related comments. The paper also illustrates the major issues of present research on use and applications of the SDMT, mostly focused on the development of methods for deriving in situ decay curves of soil stiffness with strain level and for evaluating the liquefaction potential of sands based on SDMT results.