Biologists have to be able to communicate with other biologists and be absolutely sure they are both talking about the same organism. A system of classification first proposed by Linnaeus gives them tools to do this. Recently this classification system has been further refined using studies of DNA. This program looks at how the classification system is organized and how scientific names are arrived at. The major groups of living things are explained. The dichotomous keys used by biologists to classify specimens are used and an example of constructing a key is given.