A pollen monitoring investigation has been carried out in the most important Italian olive regions (Sicily, Puglia, Calabria and Campania) to identify the behaviour of the species, characterized by many different cultivars. The present study investigated the pollination of the wind-pollinated olive trees (Olea europaea L.), continuously over a 3-year period (1999-2001) in a Mediterranean pollen monitoring network. These phases were studied using a volumetric pollen trap that aspirates known quantities of air, from which the exact volume aspirated over a certain period of time can be determined. These data were then used to determine the pollen release (daily pollen concentrations) and flowering trends in the olive groves surrounding the sites where the pollen traps were located. Solar-powered volumetric pollen traps (Fig. 1) were placed directly in the olive groves in 14 different locations. Pollen monitoring was considered to be a worthwhile source of information on flowering phenology considering olive tree reproduction starting with massive pollen emission. The principal aim of this study was to investigate the relationships between thermal trends and reproductive development in olive and the consequent olive fruit production. Numerous studies have investigated the relationship between climate and flowering phases in different species and have shown the relationship between the accumulated heat requirements and the consequent phases of pollen maturation and release. Another important aim was to investigate the influence of meteorological variables during the main olive flowering period in order to gain more the knowledge about pollen dispersion in the atmosphere. Spring temperatures expressed as Growing Degree Hours (GDH) and the flowering phases (pollination) defined as the anthesis period in olive were analysed to evaluate the cultivars that are best adapted to the particular areas and to interpret the biological response of the olive trees to more or less marked climatic variations. Through this study the main characteristics of the olive flowering phenomena in the study areas were identified (flowering period and concentration, its yearly trend). The close relationship between the meteorological variables, the heat accumulation and flowering were also shown. Large, geographically distant areas (macro-areas) were identified in which flowering was conditioned by the same meteorological variables, particularly the presence/absence of a dry climate with respect to a humid climate.