The Solarian Controversy was a debate among the proto-Overseen regarding the primacy of Celestia among the Princesses.

The veneration of Celestia was always popular from the earliest days of what would become the Overseen faith, but the question coalesced into an issue of major contention after Sunbeam began publicly preaching a simplified Princessological doctrine proclaiming that the example set by Celestia was sufficient for any pony to lead a good life. She did not exclude the other Princesses as divine, and indeed acknowledged that their veneration and examples could be equally valid, but nonetheless her opponents somewhat unfairly accused her of preaching monotheism and historical revisionism benefitting Celestia's image.

Later, Solarianism came to be used as a derogatory term leveled at sects who were accused of, if not outright dismissing other Princesses, at least placing Celestia as "first among equals" in a way that was seen to inappropriately diminish the veneration of the others. The Solarites of [[Sunshine]] and the monastic community at [[Sunshine Abbey]] were sometimes accused of Solarianism, although many of these accusations were regarded by scholars as "sour grapes" hurled by other sects jealous of the size and influence of the Sunshine community of the faithful.