To make it easier for scientists to identify and study living organisms, each organism is organised into different groups based on their similarities and differences. The grouping of organisms according to their characteristics is called taxonomy. There are eight different taxonomic groups used to classify organisms. The groups are organised in a hierarchy from largest to smallest. The first group, domain, is the most broad category whereas the last group, species, is the most specific category. These groups do not overlap with one another, so an organism which is placed in the kingdom ‘animals’ will not share the same categories as an organism which belongs to the plant kingdom.