Organisms (living things) are organized into the following categories:
Kingdom
There are 6 kingdoms of organisms: Protists, Fungi, Eubacteria, Archaebacteria, Plants, and Animals. Kingdoms are huge groups with a wide range of organisms. For example, the Plant Kingdom contains mosses but also huge oak trees. The Animal Kingdom has organisms as different as flies and people.
Phylum
The Animal Kingdom is divided into 33 phyla, including: Porifera (sponges), Cnidaria (jellyfish, corals, anemones, and hydra), Plateyhelminthes (flatworms), Arthropods crustaceans, spiders, millipedes, centipedes, and insects), Molluscs (clams, snails, slugs, nautilus, squid, and octopus), Echinoderms (starfish, sea lillies, sea urchins, sea cucumbers, and brittle stars), Annelids (polychaetes, earthworms, and leeches), and Chordates (tunicates, lancelets, and vertebrates -- this includes fish, amphibians, reptiles, birds, and mammals).
Class
There are 7 classes of vertebrate animals: Agnatha, Chondrichthyes, Osteichthyes (all of which are classifications of fish), Amphibia (amphibians), Reptilia (reptiles), Aves (birds), and Mammalia (mammals).
Order
Orders break down organisms into even smaller groups. Some Orders in the Animal Kingdom include: Primates (monkeys, apes, lemurs, people), Carnivora (carnivorous animals with pointed canine teeth and molars), Insectivora (moles, shrews, hedgehogs, all of which eat insects). Scientists disagree over what Order certain organisms belong to.
Family
Families divide organisms further. For example, the family Felidae contains all cats. Like with Orders, some scientists disagree on what Family organisms belong to.
Genus
A genus is a group of closely related species. Animals scientific names are usually given with both the genus and species. For example, Tyrannosaurus rex (Tyrannosaurus being the genus) and Panthera leo (lion) and Panthera tigris (tiger), both of which are in the genus Panthera.
Species
A species is a group of closely related organisms with similar genetic code that can interbreed. This is the most specific categroy. Two animals of the same species are more closely related to each other than two animals of the same genus, family, order, etc. if they are not of the same species.