Fluctuating asymmetry as a special kind of asymmetry can be defined as deviations from a known predetermined ratio of the parts of morphological structure under study. As a special type of phenotypic variability fluctuating asymmetry is a manifestation of ontogenetic noise or developmental variability. This type of variability is ubiquitous and plays a significant role in the observed phenotypic diversity. The level of fluctuating asymmetry turns out to be an indicator of optimal developmental conditions and genetic coadaptation. It is also considered as a parameter of fitness. Thus, fluctuating asymmetry acts as a measure of developmental stability in developmental biology and as a measure of population condition in population biology.