The biozone is the entity which allows biostratigraphy to be an independant science. Biozones represent "volumes of rock corresponding to the vertical and horizontal ranges of two or more taxa" (Opell). The best biozones are ones which display short vertical ranges and a widespread geographic distribution. Correlations are acheived by correlating biozones between locations. Depending on the scope of the study, different divisions and subdivisions of biozones can be created.

Biostratigraphic correlations are interpreted based on data obtained through the zonation of fossils. Most of the information provided by biostratigraphy is provided by the biozones.

This diagram illustrates how FAD and LAD datum is analyzed.