The animal kingdom is home to millions of different species, from tiny insects to massive whales. To make sense of this incredible diversity, scientists sort animals into groups, much like a library organizes books by genre. This system of classification is called taxonomy.

Taxonomy uses a series of ranks to narrow down an organism's place in the world. Think of it like a home address, starting with a country and getting more specific until you arrive at a single house. There are seven main ranks.

The seven major taxonomic ranks move from the most general to the most specific. They are Kingdom, Phylum, Class, Order, Family, Genus, and Species.

The Kingdom is the broadest category. For example, all animals belong to the Kingdom Animalia. The species is the most specific, referring to a group of organisms that can reproduce with one another. Let's see how this works for a familiar animal, the gray wolf.

The scientific name for an organism is a combination of its genus and species. For the gray wolf, that's Canis lupus.

One of the first and most fundamental splits in the animal kingdom is between animals with a backbone and those without. This simple difference creates two massive groups: vertebrates and invertebrates.

Vertebrates include mammals, birds, reptiles, amphibians, and fish. Invertebrates are a much larger group, covering everything from insects and spiders to jellyfish and worms.

A phylum is the next major rank after kingdom. While there are over 30 animal phyla, most animals fall into just a handful of major ones. All vertebrates belong to a single phylum, Chordata, but invertebrates are split among many.

Here are a few of the most well-known phyla:

Understanding these broad categories is the first step to appreciating the incredible and orderly diversity of the animal kingdom.