Indonesian Esoteric Buddhism or Esoteric Buddhism in Maritime Southeast Asia refers to the traditions of Esoteric Buddhism found in Maritime Southeast Asia which emerged in the 7th century along the maritime trade routes and port cities of the Indonesian islands of Java and Sumatra as well as in Malaysia. These esoteric forms were spread by pilgrims and Tantric masters who received royal patronage from royal dynasties like the Sailendras and the Srivijaya. This tradition was also linked by the maritime trade routes with Indian Vajrayana, Tantric Buddhism in Sinhala, Cham and Khmer lands and in China and Japan, to the extent that it is hard to separate them completely and it is better to speak of a complex of "Esoteric Buddhism of Mediaeval Maritime Asia." Many key Indian port cities saw the growth of Esoteric Buddhism, a tradition which coexisted alongside Shaivism.

Vajrayāna, also known as Mantrayāna, Mantranāya, Guhyamantrayāna, Tantrayāna, Tantric Buddhism, and Esoteric Buddhism, is a Buddhist tradition of tantric practice that developed in the Indian subcontinent and spread to Tibet, Nepal, other Himalayan states, East Asia, and Mongolia.