The book begins by giving a brief sequence of historical development of number and cluster theory of chemical clusters of the main group and transition metal elements. It starts with the beginning of 4N/14 Series, then the emergence of cluster number, K and later the discovery of the skeletal number of clusters. It then demonstrates how the chemical clusters can be categorized and arranged into CLAN and FAMILY series using the parameter, K_=Cy+ Dz. The book also touches on the discovery of very important cluster valence equations of the main group and transition elements and it also shows how the equations can be adjusted when the clusters have a mixture of main group and transition metal elements. In addition, it also demonstrates how isomeric structures can be constructed with the aid of the K(n) parameter. Furthermore, during the study of chemical clusters, it has been shown that a cluster composed of one or more skeletal elements comprises two parts the Cy and the Dz. This iswhat is referred to as a dichotomous relationship.