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Shaivism (/ ˈ ʃ aɪ v ɪ z ə m /; Sanskrit: शैवसम्प्रदायः, romanized: Śaivasampradāyaḥa) is one of the major Hindu traditions, which worships Shiva as the Supreme Being. One of the largest Hindu denominations, it incorporates many sub-traditions ranging from devotional dualistic theism such as Shaiva Siddhanta to yoga -orientated monistic non-theism such as Kashmiri Shaivism. It considers both the Vedas and the Agama texts as important sources of theology. According to a 2010 estimate by Johnson and Grim, Shaivism is the second-largest Hindu sect, constituting about 252 million or 26.6% of Hindus.

Shaivism developed as an amalgam of pre-Vedic religions and traditions derived from the southern Tamil Shaiva Siddhanta traditions and philosophies, which were assimilated in the non-Vedic Shiva-tradition. In the process of Sanskritisation and the formation of Hinduism, starting in the last centuries BCE, these pre-Vedic traditions became aligned with the Vedic deity Rudra and other Vedic deities, incorporating the non-Vedic Shiva-traditions into the Vedic-Brahmanical fold.

Both devotional and monistic Shaivism became popular in the 1st millennium CE, rapidly becoming the dominant religious tradition of many Hindu kingdoms. It arrived in Southeast Asia shortly thereafter, leading to the construction of thousands of Shaiva temples on the islands of Indonesia as well as Cambodia and Vietnam, co-evolving with Buddhism in these regions.

Shaivite theology ranges from Shiva being the creator, preserver, and destroyer to being the same as the Atman (Self) within oneself and every living being. It is closely related to Shaktism, and some Shaivas worship in both Shiva and Shakti temples. It is the Hindu tradition that most accepts ascetic life and emphasizes yoga, and like other Hindu traditions encourages an individual to discover and be one with Shiva within. The followers of Shaivism are called Shaivas or Shaivites.