Simultaneous　anaerobic　ammonium　oxidation　(Anammox)　and　Denitrification　(called　SAD)　holds　significant　promise　for　removing　nitrogen　and　organic　matter　from　wastewater.　Previous　studies　have　demonstrated　the　ability　of　SAD　process　and　its　emerging　extensions,　such　as　Simultaneous　Nitritation,　Anammox　and　Denitrification　(SNAD)　and　simultaneous　Anammox,　Denitrification　and　Sludge　Fermentation　(ADSF),　to　integrate　the　nitrogen　cycle　with　the　carbon　cycle.　This　study　systematically　reviews　three　types　of　SAD　process,　in　terms　of　their　microbial　groups　and　their　relationships.　Anammox　bacteria　and　denitrifiers　commonly　experience　a　symbiotic　and/or　competitive　relationship　when　treating　real　wastewater.　Biofilm　formation　and　organic　matter　limitations　are　considered　the　most　critical　conditions　for　the　co-existence　of　anammox　and　denitrification.　This　study　also　provides　an　overview　of　the　research　and　development　of　the　state-of-the-art　processes　based　on　SAD.　We　conclude　that,　while　the　optimized　performance　of　SAD　process　and　its　extensions　have　been　largely　recognized,　there　is　a　need　to　better　understand　the　mechanics,　particularly　with　respect　to　a　kinetic　and　stoichiometric　analysis.