The　global　nitrogen　cycle　is　driven　by　a　series　of　microbial　activities.　In　the　past　few　years,　the　understanding　of　nitrogen　cycling　processes　has　changed　dramatically　based　on　some　new　processes,　including　heterotrophic　nitrification,　anaerobic　ammonium　oxidation　(　Anammox)　and　archaeal　ammonia　oxidation.　In　this　review,　the　discovery,　biochemistry　mechanism　and　molecular　biology　of　organisms　linked　to　these　processes　are　presented　and　relevant　unknown　questions　are　highlighted.　A　new　nitrogen　cycle　will　only　emerge　through　considering　all　of　these　processes　and　microbial　groups　together.　In　addition,　the　paper　presents　some　new　perspectives　about　the　application　of　these　new　organisms　in　biological　nitrogen　removal　from　wastewater.　These　new　perspectives　include　enriching　heterotrophic　nitrification　bacteria　to　enhance　simultaneous　nitrification-denitrification,　enriching　Anammox　to　achieve　single-stage　autotrophic　nitrogen　removal　and　enriching　ammonia　oxidation　archaea　to　improve　nitrogen　removal　efficiency　at　low　dissolved　oxygen　(DO).