The theme of this chapter is based on the patronage of the Viṣṇuism in Odisha from c. 3^rd century BCE to c. 13^th century CE. A thorough analysis of different copper-plates and stone inscriptions along with the iconographic and architectural developments of different dynasties of Odisha have been done in order to understand the origin, continuity, development and downfall of the Viṣṇuism in Odisha. Discussions will be done how the royal patronage played a key role to give it a status as major religion. It will also focus on how Viṣṇuism was continued along with the other contemporary religious sects like Buddhism, Ṡaivism and Ṡaktism during the different dynastic periods in Odisha. Thorough discussions will be done on about the process of cult assimilation and how the autochthonous deity was became the state deity, the Lord Jagannatha.