The smallest group into which scientists classify living things is called a species.

Here's a breakdown of how classification works:

* Domain: The broadest category (e.g., Bacteria, Archaea, Eukarya)

* Kingdom: A large group within a domain (e.g., Animalia, Plantae)

* Phylum: A group of related classes (e.g., Chordata)

* Class: A group of related orders (e.g., Mammalia)

* Order: A group of related families (e.g., Primates)

* Family: A group of related genera (e.g., Hominidae)

* Genus: A group of closely related species (e.g., Homo)

* Species: The most specific group, containing organisms that can interbreed and produce fertile offspring (e.g., Homo sapiens)