A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differs from species that have been previously described or related species. For a species to be considered valid, a species description must follow established guidelines and naming conventions dictated by relevant nomenclature codes. These include the International Code of Zoological Nomenclature (ICZN) for animals, the International Code of Nomenclature for algae, fungi, and plants (ICN) for plants, and the International Committee on Taxonomy of Viruses (ICTV) for viruses. A species description often includes photographs or other illustrations of type material and information regarding where this material is deposited. The publication in which the species is described gives the new species a formal scientific name. Some 1.9 million species have been identified and described, out of some 8.7 million that may actually exist. Additionally, over five billion species have gone extinct over the history of life on Earth.

A name of a new species becomes valid (available in zoological terminology) with the date of publication of its formal scientific description. Once the scientist has performed the necessary research to determine that the discovered organism represents a new species, the scientific results are summarized in a scientific manuscript, either as part of a book or as a paper to be submitted to a scientific journal.

A scientific species description must fulfill several formal criteria specified by the nomenclature codes, e.g. selection of at least one type specimen. These criteria are intended to ensure that the species name is clear and unambiguous, for example, the International Code of Zoological Nomenclature states that "Authors should exercise reasonable care and consideration in forming new names to ensure that they are chosen with their subsequent users in mind and that, as far as possible, they are appropriate, compact, euphonious, memorable, and do not cause offence."

Species names are written in the 26 letters of the Latin alphabet, but many species names are based on words from other languages, and are Latinized.

Once the manuscript has been accepted for publication, the new species name is officially created.

Once a species name has been assigned and approved, it can generally not be changed except in the case of error. For example, a species of beetle (Anophthalmus hitleri) was named by a German collector after Adolf Hitler in 1933 when he had recently become chancellor of Germany. It is not clear whether such a dedication would be considered acceptable or appropriate today, but the name remains in use.

Species names have been chosen on many different bases. The most common is a naming for the species' external appearance, its origin, or the species name is a dedication to a certain person. Examples would include a bat species named for the two stripes on its back (Saccopteryx bilineata), a frog named for its Bolivian origin (Phyllomedusa boliviana), and an ant species dedicated to the actor Harrison Ford (Pheidole harrisonfordi). A scientific name in honor of a person or persons is known as a taxonomic eponym or eponymic; patronym and matronym are the gendered terms for this.

A number of humorous species names also exist. Literary examples include the genus name Borogovia (an extinct dinosaur), which is named after the borogove, a mythical character from Lewis Carroll's poem "Jabberwocky". A second example, Macrocarpaea apparata (a tall plant) was named after the magical spell "to apparate" from the Harry Potter novels by J. K. Rowling, as it seemed to appear out of nowhere. In 1975, the British naturalist Peter Scott proposed the binomial name Nessiteras rhombopteryx ("Ness monster with diamond-shaped fin") for the Loch Ness Monster; it was soon spotted that it was an anagram of "Monster hoax by Sir Peter S".