Abstract: The anaerobic ammonium oxidation (Anammox) process is beneficial for achieving sustainable wastewater biological treatment, which has become of great interest since its discovery. Compared with conventional nitrogen removal process, the anammox process could save oxygen consumption, operating costs required for external carbon sources, and excess sludge production. However, the growth rate of anammox bacteria (AnAOB) is extremely slow, which limits the full-scale application in wastewater treatment of the anammox process. This paper reviewed previous studies on anammox enrichment with emphasis on inoculum selection, reactor configuration, and additives stimulation. This review will help researchers in planning and designing an appropriate method for starting-up Anammox process. The findings provide theoretical guidance for the application of Anammox-based process in biological nitrogen removal.