Publisher Summary Aromaticity is regarded as the cornerstone of heterocyclic chemistry. It is largely multidimensional and scale dependent. It is noted that five and six-membered aromatic heterocycles can accommodate a π-electron sextet without appreciable strain. This chapter describes how a planar two-dimensional symmetry, with molecules, having sp2-hybridization, is achieved under the classical aromatic π-electron sextet. It also discusses some bibliographical references about the numerous existent aromatic heterocycles, with π-electron aromatic sextet. Further, the chapter discusses both the aromatic organic and inorganic cyclic structures. It is observed that the aromatic character of π-electron sextet aromatics increases stepwise from the cyclobutadiene dianion to cyclopentadiene anion, reaching a maximum with benzene, and then decreases stepwise, with the tropylium cation, and finally with the cyclooctatetraene dianion. The limits, close to which the aromaticity of the electron sextet ceases to be operative, due to various factors, such as strain, high stability of decomposition products are also discussed in this chapter.