Avalanche photodiodes (APDs) are the most popular devices in optoelectronic detecting systems. Some PIN photodiodes exhibit low noise and high bandwidth but APDs provides more sensitive characteristics relative to PIN detectors. A historical overview of the noise specifications is presented in this article. Some structures such as thin multiplication layer APDs, impact ionization engineering, ultra-low noise APD with a centered-well multiplication region and some theories such as dead space multiplication theory (DSMT) and modified DSMT (MDSMT) are reviewed.