Systematics (or biosystematics) is the classification of living organisms into natural, ordered in a hierarchical (or layered) fashion that emphasizes their phylogenetic (or evolutionary) relationships. Systematics is related to taxonomy, although the latter is more directly concerned with the theory and practice of naming and describing species and other taxonomic units (or taxa).

Modern systematists believe that all organisms can be divided into five major group, known as kingdoms ( these represent the highest level in the systematic organization of life. The five kingdoms are:

• Monerans, including bacteria and cyanobacteria (or blue-green bacteria), which are the simplest organisms, being single-celled and lacking a membrane-bounded organelle called a nucleus (i.e., they are prokaryotes; all other kingdoms have a nucleus, and are eukaryotes).
• Protista, encompassing a wide diversity of simple, eukaryotic organisms, including unicellular and multicellular species of protozoans, foraminifera, slime moulds, single-celled algae, and multicellular alga.
• Fungi, including yeasts...