God the Sustainer is a theological term referring to the concept of a God who sustains and upholds everything in existence. It is used mostly in Christian and Islamic theology. It is held that as the creator who gives being and existence to his creatures which he created from nothing, God continues to provide the same being and existence to his creatures which do not have being in themselves. Thus creatures are totally dependent on God and would vanish without his conserving action.
In pantheism and pandeism (pantheistic deism) generally God or some similar formulation is characterized as only needing to exist as a sustaining force, with no other aspect.
Christian Theology 
In the Christian theology, the described doctrine is supported by the following biblical and Deuterocanonical references:
- Wisdom 11: 21-26: “For you love all things that exist, and detest none of the things that you have made; for you would not have made anything if you had hated it. How would anything have endured, if you had not willed it? Or how would anything not called forth by you have been preserved? You spare all things, for they are yours, O Lord, you who love the living.”
- John 5:17: My Father works until now and I work.
- Hebrews 1:3: He upholds all things by the word of his power
Moreover, there are other relevant places in the doctrinal Christian literature, for example:
- St. Augustine comments on John 5:17: Let us therefore believe that God works constantly, so that all created things would perish, if his working were withdrawn.
- The Catechism of the Catholic Church says in 301: With creation, God does not abandon his creatures to themselves. He not only gives them being and existence, but also, and at every moment, upholds and sustains them in being, enables them to act and brings them to their final end. Recognizing this utter dependence with respect to the Creator is a source of wisdom and freedom, of joy and confidence: