This paper will briefly summarize the methodology employed in constructing a definition of what the believer’s union with Christ actually is. After noting the need for a methodological approach in the introduction due to the multitude of models proposed since the Reformation, the first main content section will discuss the “creational solidarity” between God the Son and all of creation. Colossians 1:15–21 will be the key text to show that all creation is located in God the Son and that he is the one in whom, for whom, and through whom it both exists and consists, The second section will discuss the incarnation, as the creator and sustainer of all creation assumes human nature into himself and thereby creates a natural, “anhypostatic” solidarity with all humanity in his incarnate existence. The third section will discuss Jesus’ personal assumption of death into himself at the crucifixion, becoming at once both the judge of the world and the one who is judged. Because he is God and life, death cannot hold him and he rises, elevating humanity into a new sphere of existence in immortality, impeccability, and incorruptibility. As Adam is the head of the original human race (Humanity 1.0), Jesus becomes the head of the new one (2.0), sharing the properties of the new and raised human nature with all the faithful. Once this methodological background is complete, I propose the following definition of union: “It is a perichoretic union (meaning mutual indwelling and mutual activity in the other) of two persons, Christ and the believer (and by extension all believers), based upon a shared nature (though only compatible now as we are still in Humanity 1.0) guaranteed by a common source (Adam in 1.0, the resurrected and glorified Christ in 2.0), possessing a common faculty of will unalterably oriented toward the telos of creation, and made possible by the resurrected and ascended Christ becoming a life-giving spirit capable of sharing a location in time-space-matter with multiple human persons simultaneously, all the while grounded in the creational and anhypostatic solidarity of God incarnate and his personal identification with his own creation in death and resurrection.” The paper as a whole will be a methodological progression to arrive at the working definition.