This book discusses the analysis and categorization of zintl phases or clusters using the K(n) parameter and skeletal valency. The skeletal valency of an element has been found to be interrelated with its atomic number Z through its skeletal number K. The zintl ion clusters, just like any others, can be decomposed by skeletal numbers of its elements to generate corresponding K values. Since a cluster has a specific number of skeletal elements n, if its cluster number K is known, then we have a very important K(n) parameter. This parameter can be utilised to construct an isomeric structure of the cluster and its cluster valence electrons can be derived from it. The K(n) parameter also can be transformed into cluster series S=4n+q, using the series of the cluster we can derive the corresponding borane cluster analogue or any other cluster such as transition metal carbonyl or hydrocarbon analogue. The geometrical structures of zintl ions are clearly related to the structures of the corresponding analogues.