The aim of this paper is a new synthesis of the results obtained in Italy and in the surrounding areas during more than thirty years (1956-1987) by the seismic exploration method of wide angle reflection - refraction generally known as DSS--Deep Seismic Soundings. Italy is among the countries most intensively surveyed by this method. During the long period of application, the techniques experienced remarkable modifications with regard to the instrumentation (from analog to digital), the acquisition procedures (density and type of layouts), as well as processing and interpretation (ray-tracing and modelling). Despite the low resolving power and the constraints given by the large distance between the shots and by the low density of recorders, the method is particularly well-suited to describe the pattern of the crust-mantle boundary and is the unique way to obtain the distribution of the seismic velocity in the lower crust. A rich literature was produced both during and after the long period of data acquisition. However, we feel that a further comprehensive survey, compiled using homogeneous criteria, could be useful to discuss and update the geodynamic schemes of the central Mediterranean. We have prepared synthetic cross-sections based on the most reliable interpretations and compiled using homogeneous criteria of presentation. A new map of the Moho boundary is also presented. In addition to the depth contour lines of the boundary, which show the complexity of the deep structure, we also describe the crustal types found in the area: besides the two main interacting domains of the Adriatic and European plates, the oceanic-sub oceanic type is present in the Ligurian and Tyrrhenian seas. Moreover, a further type is defined: the Ligurian-Tuscan-Peri-Tyrrhenian strip of a thinned, anomalous crust. The thickness and structure of this intermediate crustal type was produced by a multi-phase geodynamic evolution: in the area beneath the Ligurian sea, Corsica and Tuscany, by the opening of the Provencal Basin and the counter clockwise rotation of the Sardinian-Corsican microplate; in the south, by the opening of the Tyrrhenian sea. The structure of the crust-mantle boundary and of the lower crust beneath the Alpine range is outlined in detail, clearly revealing the contrast between the fairly homogeneous European crust beneath the central Alps and the complex northern and north western edge of the Adriatic-Padan crust; the latter is witness to the effect of the push-and-pull stages responsible of the Alpine evolution.