The distribution of planctonic living species of Foraminifera is conditioned by environmental factors such as temperature, salinity and oxygen content of water; thus the composition of foraminiferal faunae provides information about prevailing climatic conditions. Fossil foraminifera also can be utilized as ecological indicators, but the reconstruction of past environments becomes more and more inaccurate as we go back toward the Cretaceous period, when the group appeared. Here we present three paleoecological examples. The first one concerns the reconstruction of Mediterranean climate during Late Pleistocene. It is based on investigation on open sea sediments in which layers of volcanic ashes alternate with layers of sapropel. Both studies on relative composition in microfossils and studies on ratio between14O and16O fixed in foraminiferal shells allow to recognize climatic fluctuations. The second example deals with effects of Messinian salinty crisis in Mediterranean sea and concerns some lineages ofGloborotaliaewhich were interrupted by deposition of evaporites. The third example concerns a study on associations of planktonic Foraminifera embedded in several stratigraphic samples of Paleogene, collected in shallow and deep bottoms of Atlantic Ocean.