In this paper we observe that recent voltage problems, including August 2003 blackout, are often caused by the lack of adequate and timely information. We study the type of information essential to avoiding such problems in the future. The needed information concerns (a) choice of a performance index characterizing problems of interest; (b) information structure necessary to monitor the performance index with acceptable accuracy; and, (c) the interdependence between (a) and (b). We propose a novel performance index and corresponding information structure. This information structure requires very little or no communications between decomposed subsystems. Illustrations of proposed concepts in multi control area systems are presented. These findings form a basis for grid modernization through communications and computing for improved voltage support in multi control area system.