Classification systems attempt to solve the problem of providing meaningful groupings of organisms.  The Swedish scientist, Carolus von Linnaeus, is credited with introducing binomial nomenclature and hierarchical classification as an organized way of naming and describing organisms and their relationships to one another.  Binomial nomenclature refers to the use of a two-part name for each species (one name designating genus and one designating species).

Linnaeus described a hierarchical classification system using seven taxonomic categories, or taxa (Kingdom, Phylum, Class, Order, Family, Genus, Species).  Beginning with species, each category becomes progressively more comprehensive.  For example, while the leopard, tiger and domestic cat all belong to different genera, they are grouped together in the same family.

Taxonomy is the science of classification.  When taxonomic systems include hypothesized evolutionary relationships among groups, the field generally is referred to as Phylogenetics.  Systematics is a larger field involving classifying organisms based on their phylogenetic relationships.  Systematics can be thought of as the study of biological diversity and how that diversity evolved.  In a sense, Charles Darwin introduced systematics in his revolutionary work, The Origin of Species.  He wrote, "The natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical" (Darwin, 1859).

Early naturalists identified plants and animals by observable structural similarities and referred to organisms using long complicated phrases.  This was known as the "polynomial system."  In this system, a plant might be described by phrases of 12 or more words.  It is not surprising that polynomial names could become very complex and were often misinterpreted when translated from one language to another.

In the 1700s, Carolus von Linnaeus, sometimes referred to as the Father of Classification, described a binomial system, which was published in his early work, System Naturae (1735).  Although he created the two-word system as a short-cut for users of this work, the system was rapidly adopted as a manageable way of naming species.  
 
In the binomial nomenclature system, genus and species-just two names-replace the long string of words used in the polynomial system.  The meaning of words can differ from language to language and from country to country.  For example, in Great Britain, the word "buzzard" refers to an organism Americans call a hawk.  For this reason, scientific names are written in Latin to maintain a uniform system of naming across all languages.

In the binomial system, genus is always a noun, underlined (or italicized), and capitalized; species is a descriptive term, underlined (or italicized), and not capitalized.  Some examples of binomial names include: Quercus rubra (red oak), Panthera pardus (leopard), or Homo sapiens (human).

Carolus von Linnaeus created a hierarchical classification system using seven taxonomic categories, or taxa (Kingdom, Phylum, Class, Order, Family, Genus, Species).  These categories are based on shared physical characteristics, or phenotypes, within each group.  Beginning with kingdom, each successive level of classification becomes more and more specific.  Organisms within the same order have more in common with one another than organisms within the same class. For example, all species of bears are mammals, but not all mammals are bears.  A useful pneumonic tool to help students remember the hierarchical classification system is: "King Phillip Came Over For Green Soup," with the first letter of each word representing each category, beginning with kingdom and ending with species.