15 physical and chemical processes responsible for the phenomenon of color are described. The 15 causes are subdivided into five categories; vibrations and simple excitations; transitions involving ligand field effects; transitions between molecular orbitals; transitions involving energy bands; geometrical and physical optics. The principles behind each of the causes of color are explained. Examples of each type of process are given and illustrated in color. The article forms an introduction to the subject, which is covered in greater detail in the author's book of the same name. -- AATA