The mythology of Indonesia is very diverse, the Indonesian people consisting of hundreds of ethnic groups, each with their own myths and legends that explain the origin of their people, the tales of their ancestors and the demons or deities in their belief systems. The tendency to syncretize by overlying older traditions with newer foreign ideas has occurred. For example, the older ancestral mythology might be merged with imported mythology, such as Hindu, Islam, or Christian biblical mythology.

Some native Indonesian ethnic groups that were isolated from the rest of the world until recent centuries have their own native myths and gods. These native mythologies are relatively free from foreign influences, such as Pamonas, Torajans, Nias, Bataks, Dayaks, Moluccans, and Papuans. By contrast, Javanese, Balinese, and Sundanese were influenced by Hindu-Buddhist Indian mythology as early as the 1st century CE. Hindu gods, legends and epics such as Ramayana and Mahabharata were adopted and adapted into a uniquely local form.

Many Hindu-Buddhist mythical beings have a role in Sundanese, Javanese, and Balinese mythology, including of Hindu gods and heroes, devatas, asuras, apsaras (known as hapsari or bidadari), kinnaras, etc., while native gods of nature such as Semar, Dewi Sri, and Nyai Roro Kidul are either given identified as their Hindu counterpart or incorporated into a Java-Bali Hindu pantheon unknown in India. For example, native rice goddess Dewi Sri is identified with Lakshmi the shakti of Vishnu, and Semar and his sons the Punakawans are incorporated into the epic of Mahabharata in Javanese wayang kulit, as the clown servants of the Pandawas. Several names refer to gods, such as dewa (devas), dewi (devi), dewata (devatas), and in native traditions usually referred to as Batara (male god) and Batari (female goddess). These names are similar to the native Philippines mythology of Bathala and Diwata.

After the coming of Islam to the Indonesian archipelago, Islamic mythology especially those dealing with spiritual beings, such as devils, demons, jinns and angels entered Indonesian mythology. In Sumatra, Malay, Aceh, and Minangkabau mythology was almost entirely supplanted by Islamic mythology. However, belief in local spirits such as the forest guardian, the ghost of water or haunted places still exists, often associated with a jinn or the tormented soul of a deceased human.

Creation myths explain the creation of the universe and the world and its lands. They often explain the story of their ancestors. Most native Indonesian ethnic groups, especially those not influenced by other traditions, explain the origin of the universe, gods and deities, as well as their ancestors.

Ancient people in Java and Bali believed in an unseen spiritual entity that has supernatural powers identified as Hyangs. This spirit can be either divine or ancestral. The reverence for this spiritual entity can be found in Sunda Wiwitan, Kejawen, and Balinese Hinduism.

According to the myth of some ethnic groups in Sulawesi, the earth sat upon the back of gigantic babirusa. An earthquake happened when the boar felt itchy and rubbed its back against a gigantic palm tree. This myth has its counterpart, in the Hindu myth of Varaha, the third avatar of Vishnu as a gigantic boar that carried the world upon his back.

The Dayak indigenous religion, Kaharingan, is a form of animism. The Dayak arose from middle-earth out of a cosmic battle at the beginning of time between a primal couple, a male and female bird/dragon (serpent). Representations of this primal couple are among the most pervasive motifs of Dayak art. The primal mythic conflict ended in a mutual, procreative murder. The body parts became the present universe stage by stage. This primal sacrificial creation of the universe is re-experienced and ultimately harmoniously brought together in the seasons of the year, the interdependence of river (up-stream and down-stream) and land, the tilling of the earth and fall of the rain, the union of male and female, the distinctions between and cooperation of social classes, the wars and trade with foreigners, indeed in all aspects of life, even including tattoos on the body, the lay-out of dwellings and the annual cycle of renewal ceremonies, funeral rites, etc. The practice of Kaharingan differs from group to group, but shamans, specialists in ecstatic flight, are central to Dayak religion. They bring together the various realms of Heaven (Upper-world), earth and Under-world, for example healing the sick by retrieving their souls while they journey to the Upper-world land of the dead, accompanying and protecting the soul of the dead, presiding over annual renewal and agricultural regeneration festivals, etc. Death rituals are most elaborate when a noble (kamang) dies. On particular religious occasions, the spirit is believed to descend to partake in celebration, a mark of honour and respect to past ancestors and blessings for a prosperous future.