Diksa (Sanskrit: दीक्षा in Devanagari, dīkṣā, Tamil: தீட்சை) also spelled deeksha or deeksa in common usage, translated as a "preparation or consecration for a religious ceremony", is giving of a mantra or an initiation by the guru in Indian religions such as Hinduism, Buddhism, and Jainism. Diksa is given in a one-to-one ceremony, and typically includes the taking on of a serious spiritual discipline. The word is derived from the Sanskrit root dā ("to give") plus kṣi ("to destroy") or alternately from the verb root dīkṣ ("to consecrate").When the mind of the guru and the disciple become one, then we say that the disciple has been initiated by the guru.

Diksa can be of various types, through the teacher's sight, touch, or word, with the purpose of purifying the disciple or student. Initiation by touch is called sparśa dīkṣā. The bestowing of divine grace through diksa is called śaktipāt.

Vishnu Yamala (tantra) says: "The process that bestows divyam jnanam (transcendental, spiritual knowledge) and destroys sin (pāpa), the seed of sin and ignorance, is called diksha by the spiritual persons who have seen the Truth (desikais tattva-kovidaih)."