Irenaeus of Lyons is one of the earliest theologians from whom we have retained a somewhat substantial body of work, and I agree with John Behr that "It would be hard to overstate the importance of Irenaeus of Lyons, both with respect to what came before him and for the history of Christian theological reflection and identity thereafter" (Irenaeus of Lyons: Identifying Christianity, Oxford 2013, p. 205). And yet Irenaeus' eschatology has been controversial and often overlooked or downplayed. In the manuscript tradition and in the various editions of his writings published since the reformation, certain eschatological passages from book 5 of Adv. haer. were excised or overlooked. With the Source Chretiennes-edition, this has changed, due to the inclusion and translation of passages in book 5 only found in the Armenian translation discovered in 1904. Some of these passages cast better light on Irenaeus' eschatalogy, in particular on his understanding of the "Kingdom of the Son", which perhaps can be equated with the millenial kingdom. In this short communication, I would like to briefly explore the role this eschatological earthly "Kingdom of the Son" plays in Irenaeus' theology, in particular as this is related to his overall vision of the telos of humanity. The "Kingdom of the Son" is for Irenaeus precisely the time and place where humans are to "practice" participation in God and growth in his likeness. As such, it is an integral part of his theology, not something he adopted halfheartedly from Papias or other "fathers".