The California Current System has been referred as the most intensively studied oceanic system in the world. Since 1997, in the southern California Current region, the IMECOCAL Program has conducted quarterly oceanographic cruises whit an average of 80 stations following the original CalCOFI Program sampling grid. In each station CTD cast are made. Bongo-net hauls are carried out to determine biomass and structure of the zooplankton community. A total of 63 cruises have been conducted, accomplishing 15 fall cruises, 17 winter cruises, 16 spring cruises and 15 summer cruises. The oceanographic structure has been characterized, as a transitional zone where the relatively cold and low-salinity water of the California Current meets warmer and more saline tropical and subtropical waters. Distribution of the correspondent biota from this different type of water masses are affected mostly by seasonal and interannual variability. According to this, fish larvae communities divide the region in three mayor zones: ENSENADA, between Ensenada, BC and Punta Baja (CalCOFI lines 97 to 110), defined by a lower larval diversity of mostly subartic and temperate taxa; VIZCAINO BAY, and the adjacent oceanic region (CalCOFI lines 113 to 127), whit the highest larval diversity in the region, were biota of northern and southern taxa coincide, and SOUHT PUNTA EUGENIA, which is the less sampled area, but most of the time includes sampling stations in the Gulf of Ulloa and north Bahía Magdalena (CalCOFI lines 130 to 137). Fish larvae of tropical and subtropical taxa are dominant in this area.