The word Entomology has been used since Aristotle (384-322 BC) to denominate the science concerned with the study of the insects. Entomology is a combination of the Greek suffix logos, 'the study of' and the Greek root word entomos, meaning 'insect' [en- ("in") + tomos ("cutting" - a reference to the insect's segmented body)]. The word 'insect' comes from the Latin "Animal Insectum", an animal with a segmented body.

There are over one million described species of insects. These are divided into 29 orders, of which Coleoptera (beetles), with 125 families and ca. 500,000 described species, is the largest. In fact, one of every four animal species on the planet is a beetle.

Insects are small in size, but can be found in amazing numbers. Some researchers believe that ants make up 30% of all animal biomass in the Amazon basin and that 10% of the world's animal biomass is comprised of termites. Astonishingly, 20% of the planet's animal biomass is made up of social insects.

There is no land on earth where insects cannot be found. Even the North and South Poles have insect inhabitants. Insects can be found in such surprising places as Lake Mono (California, USA), whose salinity is close to that of the Dead Sea (larvae of the fly Ephydra hyans), in pools of crude oil in California oilfields (larvae of the fly Psilopa petrolei) and even in Iceland's hot springs, where temperatures reach 48 degrees Celsius (larvae and adults of the fly Scatella thermarum).

Despite their success on land, however, very few insects (less than 400 species) have managed to colonize the marine environment. Most of these insects, mainly flies and beetles, are found in tide pools, on beaches and in marshes. Only a select few (i.e. some Halobates water striders) live on the surface of the open ocean (pelagic species).

Regardless of huge diversity and abundance of insects, estimates indicate that just less than 1% of described insect species interact with mankind. Nonetheless, ca. 33% of all food produced in the world is consumed by insects, despite the control measures taken against them. Several diseases are vectored by insects; vector-borne diseases were responsible for more human disease and death in the 17th through the early 20th centuries than all other causes combined, and malaria (vectored by mosquitoes) still kills millions of people to this date. Insects are also a major cause of mortality and reduced productivity in livestock, by feeding on or parasitizing livestock, or indirectly, by transmitting livestock diseases.

Their detriment to agriculture, livestock and men, makes them one of the most economically-important organisms in the world.