On the Holy Spirit is a theological treatise by Basil the Great, bishop of Caesarea and one of the Cappadocian Fathers. It presents a lucid and edifying appeal to Scripture and early Christian tradition in order to prove the divinity of the Holy Spirit. St. Basil forms clear and careful arguments against heresy of the early Christian church, mainly the second wave of Arianism. Basil proves that the Holy Spirit and the Son are not, by any margin, lesser in divinity than the Father, placing his defense of the doctrine of the Holy Spirit within the tradition of the Church.

Basil the Great (330-379) was a Greek bishop of Caesarea Mazaca in Cappadocia. He was an influential theologian who supported the Nicene Creed and opposed the heresies of the early Christian church. Basil, Gregory of Nazianzus, and Gregory of Nyssa are collectively referred to as the Cappadocian Fathers. The principal theological writings of Basil are his On the Holy Spirit, a lucid and edifying appeal to Scripture and early Christian tradition, and his Refutation of the Apology of the Impious Eunomius.