The　efficiency　of　wastewater　treatment　practices　can　be　significantly　improved　through　the　introduction　of　new　microbial　treatment　technologies.　In　order　to　meet　increasing　stringent　discharge　standards,　new　applications　and　control　strategies　for　the　sustainable　removal　of　ammonium　from　wastewater　have　to　be　implemented.　Partial　nitrification　to　nitrite　was　reported　to　be　technically　feasible　and　economically　favorable,　especially　when　the　wastewater　with　high　ammonium　concentrations　or　low　C/N　ratios　was　treated.　For　successful　implementation　of　the　technology,　the　critical　point　is　how　to　maintain　the　partial　nitrification　of　ammonium　to　nitrite.　Nitritation　can　be　obtained　by　selectively　inhibiting　the　nitrite　oxidizing　bacteria　through　appropriate　regulation　of　the　system＇s　DO　concentration,　microbial　SRT,　pH,　temperature,　substrate　load,　operational　and　aeration　pattern,　inhibitor　and　so　on.　This　review　addresses　the　microbiology,　its　consequences　for　application,　the　current　status　regarding　application,　and　its　future　developments.