Hinduism () is an Indian religion or dharma, a religious and universal order or way of life by which followers abide. As a religion, it is the world's third-largest, with over 1.2–1.35 billion followers, or 15–16% of the global population, known as Hindus. The word Hindu is an exonym, and while Hinduism has been called the oldest religion in the world, many practitioners refer to their religion as Sanātana Dharma (Sanskrit: सनातन धर्म, lit. ''the Eternal Dharma''), a modern usage, which refers to the idea that its origins lie beyond human history, as revealed in the Hindu texts. Another endonym is Vaidika Dharma, the dharma related to the Vedas.

Hinduism is a diverse system of thought marked by a range of philosophies and shared concepts, rituals, cosmological systems, pilgrimage sites, and shared textual sources that discuss theology, metaphysics, mythology, Vedic yajna, yoga, agamic rituals, and temple building, among other topics. Prominent themes in Hindu beliefs include the four Puruṣārthas, the proper goals or aims of human life; namely, dharma (ethics/duties), artha (prosperity/work), kama (desires/passions) and moksha (liberation/freedom from the passions and the cycle of death and rebirth), as well as karma (action, intent and consequences) and saṃsāra (cycle of death and rebirth). Hinduism prescribes the eternal duties, such as honesty, refraining from injuring living beings (ahiṃsā), patience, forbearance, self-restraint, virtue, and compassion, among others. Hindu practices include worship (puja), fire rituals (homa/havan), devotion (bhakti), fasting (vrata), chanting (japa), meditation (dhyāna), sacrifice (yajña), charity (dāna), selfless service (sevā), learning and knowledge (jñāna), recitation and exposition of scriptures (pravacana), homage to one's ancestors (śrāddha), family-oriented rites of passage, annual festivals, and occasional pilgrimages (yatra). Along with the various practices associated with yoga, some Hindus leave their social world and material possessions and engage in lifelong Sannyasa (monasticism) in order to achieve moksha.

Hindu texts are classified into Śruti ("heard") and Smṛti ("remembered"), the major scriptures of which are the Vedas, the Upanishads, the Purānas, the Mahābhārata, the Rāmāyana, and the Āgamas. There are six āstika schools of Hindu philosophy, who recognise the authority of the Vedas, namely Sānkhya, Yoga, Nyāya, Vaisheshika, Mimāmsā, and Vedānta. While the Puranic chronology presents a genealogy of thousands of years, starting with the Vedic rishis, scholars regard Hinduism as a fusion or synthesis of Brahmanical orthopraxy with various Indian cultures, having diverse roots and no specific founder. This Hindu synthesis emerged after the Vedic period, between c. 500–200 BCE and c. 300 CE, in the period of the Second Urbanisation and the early classical period of Hinduism, when the Epics and the first Purānas were composed. It flourished in the medieval period, with the decline of Buddhism in India.

Currently, the four major denominations of Hinduism are Vaishnavism, Shaivism, Shaktism, and the Smarta tradition. Sources of authority and eternal truths in the Hindu texts play an important role, but there is also a strong Hindu tradition of questioning authority in order to deepen the understanding of these truths and to further develop the tradition. Hinduism is the most widely professed faith in India, Nepal, Mauritius and in Bali, Indonesia. Significant numbers of Hindu communities are found in other countries of South Asia, in Southeast Asia, in the Caribbean, Gulf states, North America, Europe, Oceania, Africa, and other regions.