It is the most important general concept in organic chemistry that the π electron delocalization is stabilizing. However, this concept, together with the ability of the π electron delocalization to level out of differences in bond lengths between formal double and single bonds, the Huckel 4N＋2 theory, and the high stability of the π system in benzene, was argued during the period of 1930's through 1990's. The compounds, such as star-phenylene, linear and angular N- phenylene, tris(tri-carbonylironcyclobuta-dieno)benzene, 2,7-di-tert- butyl-4,5,9,10-tetraphenylbenzo-1,2,4,5 dicyclobutadiene were synthesized, and their crystallographic data were brought up as the experimental examples. these experimental results appear to support Shaik's viewpoint. On the other hand, the role of Mills-Nixon distortion in triannelated benzene was doubted by Siegel, and the stabilizing effect of the π electron delocalization in benzene was reconfirmed by the Streitwieser. Meanwhile, various methods for energy partition, such as those of Morokuma, Shaik, Kollma, Jug, Streitwieser, Wolfe and Ichikawa, were reviewed and commented. Kollma's and related methods, in which the effects of the π electron delocalization on the π framework and on the Fock matrix have been neglected completely, were questioned. At last, our novel energy partition was introduced. More than 50 references were cited.