ABSTRACT: Reefs have long been subject of considerable, interest for their importance in carbonate depositional systems » sea-level changes,, paleontology and hydrocarbon: exploration, at present there exist a large amount of information on reefs •and refold carbonate bodies in `the. related literature. The aim of this paper is to provide an. introductory review on. reefs to contribute towards reef studies. Reef is a rigid.,, wave resistant organic structure, mainly built by large, frame building skeletal metazoans (corals and corralinie algae) .and the associated accessory organisms, such, as encrusting foraminifers, calcareous algae, bryozoas,,, mollusk., sponges etc, that act as fr.amebin.ders and sediment producers. Reefs, develope at the well-lighted, aerated., nutrient-rich,,, warm .and shallow waters- of the stable sheld seas and carbonate platforms of passive- continental margins. Reef growth and development is controlled by a number of physical, and. biological factors including nature of the reef building, organisms, underlying topography» sea-level changes and wave energy. Reefs, though differing in shape -and. dimensions, form topographic highs with, a well-developed as.symmelxi.cal cross-profile characterised by morphological and ecological, zones and the associated, faciès.. Reefs, evolved, through the geological time from Precambiran-Early Paleozoic stromatolite buildups through Mesozoic reefs with Tubiphytes and coral-algal communities .and rudistid reefs to Tertiary .and Modem organic framework, built by heraiatypic scleractinnian corals and coralline algae.