Ayyappan (Malayalam: അയ്യപ്പന്‍,Tamil: ஐயப்பன்) (also called Sartavu, or Sasta) is a Hindu deity worshiped in a number of shrines across southern India. Ayyappan is believed to be an incarnation of Dharma Sasta, who is the offspring of Shiva and Vishnu (as Mohini, in his female form) and is generally depicted in a yogic posture, wearing a bell around his neck. Ayyappan may bear a historical relationship to the tutelary deity Aiyanar in Tamil Nadu.

By the 20th century, there has been an increase in the number of worshipers of Ayyappan from many different groups, spurred by vast improvements in transport and communication in southern India.

Ayyappan's annual festival is a time of pilgrimage for ever-growing numbers of men from throughout South India. The most prominent and famous Ayyappan shrine is the one at Sabarimala, in the hills of Pathanamthitta in Kerala, with over 30 million devotees visiting it every year, making it one of the largest pilgrimage sites in the world. These devotees fast and engage in austerities under the leadership of a teacher for weeks beforehand and then travel in groups to the shrine for a glimpse of Ayyappan. Bus tickets are hard to obtain for several weeks as masses of elated men, clad in distinctive ritual dhotis of various colors, throng public transportation during their trip to the shrine.