In the article, the author discusses Jesus’ intitulation of God as Abba and its impact on the idea of God’s fatherhood in the New Testament writings. Responding to the recent criticism of J. Jeremias’s theses (cf. B. Chilton, M.R. D’Angelo), he tries to show that without the initial source, which was Jesus of Nazareth and his public teaching, the dynamic expansion of the idea of God’s fatherhood in the New Testament would not be possible. After a brief presentation of J. Jeremias’s ground-breaking opinion on Jesus’ filial relation to God as Father, encapsulated in the “Abba, Father” cry (Mk 14:36), a second section analyses the texts of the Hebrew Bible and Second Temple Judaism that explore the theological idea of God as Father. The third part focuses on the NT witnesses to God’s fatherhood, i.e. God both as the Father of Jesus Christ and the Father of all believers (υἱοθεσία). In conclusion, the literary evidence preserved in the NT writings and rational arguments point to Jesus of Nazareth as the source and starting point of the NT idea of God’s fatherhood. Jeremias’s study is still valid, and the address “Abba-Father” uttered by the historical Jesus remains the most concise and fullest expression of his filial relation to God.