The nitrogen element, which constitutes 75.5% by weight and 78.06% by volume of the Earth's atmosphere, participates in the structure of many important biomolecules such as ATP, chlorophyll, nucleic acids and vitamins. However, this element found as a form of dinitrogen gas (N2) is not suitable form to use for living organisms, especially primary producers. Therefore, the nitrogen cycle is one of the most important biological processes that ensure the continuity of life. At the end of the 1990’s, findings on the nitrogen cycle were updated along with the discovery of anammox bacteria, and anammox applications have now become an alternative technology to conventional nitrification/denitrification processes used in wastewater treatment plants. This process can be explained as a conversion of ammonium into the dinitrogen gas in anoxic environment by anamox bacteria using nitrite as an electron acceptor. Although seven anammox genera have been discovered up to now, all of them are named by the status of Candidatus since their pure cultures cannot be obtained. Furthermore, these bacteria have been a scientific turning point in the fields of ecological research and molecular biology due to their unique metabolism. In this context, the growth and cell biology, molecular mechanism of anammox bacteria and the role and importance of Anammox process in environmental applications were investigated in detail.