Taxonomy is the science of grouping and organising species in a coherent classification system, which reflects established evolutionary relationships, whereas systematics or phylogenetics is the science of inferring evolutionary relationships. These tasks overlap, and the terms taxonomy and systematics are often used interchangeably with little distinction. Nomenclature is a purely technical convention to provide maximum universality and continuity in the naming of organisms, except where taxonomic reasons dictate otherwise. Internationally accepted codes of nomenclature are meant to guide only the naming of organisms, leaving full freedom to taxonomic research.

The biota is classified according to a hierarchical system, which can be compared to a branching tree. The root of this tree corresponds to all species on Earth, which branch into increasingly smaller and more specific classification levels: domain, kingdom, phylum, class, order, family, genus, and species.

In the search on the web it is possible to search for species or other classification levels by using latin or Icelandic names and limit the search to Biota. Species fact sheets available on the IINH website are mainly in Icelandic. Pages on birds and mammals include English summaries. Fact sheets for many marine invertebrates are in English only.