Stable isotopes are elements with the same number of protons but different number of neutrons.The stable isotopes of oxygen, carbon, and nitrogen are useful to reconstruct the past climatic and oceanographic changes. Besides, the oxygen isotopic stratigraphy of marine sediments provides a robust time frame work to correlate widely separated marine sections and also to correlate the paleoceanographic and paleoclimatic events. This helps us to interpret the cause and effect relationship among various events recorded in diversely located stratigraphic columns. The stable isotopic studies have become thus one of the most important tools in paleoceanographic and paleoclimatic studies. The aim of the paleoclimatology is far beyond the plain documentation of past climate changes. It will improve our understanding of the mechanism of climate variability including abrupt climate changes, especially under the greenhouse gases forcing expected toward the end of the century.Stable isotope probing (SIP) is a relatively new technique that is still being developed and refined.