The Italian active volcanoes are located in the southern part of the national territory. The island of Sicily hosts one of the most famous worldwide active volcanoes (M. Etna), while most of the surrounding islands are active volcanoes; among these there are volcanoes having almost continuously activity, such as Stromboli, or volcanoes which last eruption occurred during last centuries, such as Vulcano or Pantelleria. Owing to the high population density close to these volcanoes, the volcanic risk is considerable; indeed a large part of the researches performed during the last decades have been aimed at improving the capability to evaluate the volcanic hazard by constantly upgrading the geophysical monitoring systems, for instance, by enlarging the areas covered by the networks (seismic, geodetic, etc.), by increasing the number of the sensors in the monitored areas and by implementing new technologies. In this framework, the geodetic systems represent a good example of the improvement in the monitoring systems. Never used on Sicilian volcanoes before the 1970's, nowadays they represent one of the main pillars of the volcanic monitoring systems. After an initial use of classic geodetic techniques (distancemeter and levelling) during the mid-70's, the first permanent tilt networks were installed on Mt. Etna and Vulcano throughout the 70's and 80's and continuously updated up to now. The introduction of the GPS in the research activities at the end of the 80's allowed to connect the already existing geodetic networks on the volcanoes and to link these to areas considered stable with respect to the volcanoes, allowing to measure "absolute" displacements due to the volcanic activity for the first time. The capability of GPS receivers to be remotely controlled, has allowed implementing several permanent networks that now provide a continuous flux of information (@ 1 Hz) on the dynamic of the Sicilian volcanoes. The start of the ERS-SAR interferometric missions provided new and intriguing data relevant to the ground deformation pattern of Mt. Etna, which is now one of the most "shouted" volcano of the world. To integrate these different data sets specific software were implemented and applied to several cases of study offered by the different volcanoes. These studies have widely improved the knowledge both on the structure and the dynamics of the Sicilian volcanoes, allowing a more efficient and effective exploitation of the geodetic monitoring systems for an effective evaluation of the volcanic hazard. During the last decades, several examples of this fruitful feedback between research and monitoring activities have been provided during eruptions or volcanic crisis. Among these, we discuss some instructive examples relevant to Mt. Etna, Pantelleria and Aeolian arc.