OzTAM was created in 1999 after the Seven and Ten Networks led a call for a re-tendering of the contract to provide audience ratings. Executives from both networks were concerned that the previous ratings service did not accurately reflect viewing levels for their channels. 
Prior to OzTAM, the dominant metropolitan ratings company was Nielsen Media Research. The two companies competed for a short time, before Nielsen pulled out. Nielsen continues to be active in some regional areas.
There are ten official survey periods, of four weeks each, cover 40 weeks of the year, excluding 2 weeks over Easter and 10 weeks over summer.