In the philosophy of the Neoplatonic philosopher Plotinus, the doctrine of conversion plays a vital role in the metaphysics of emanation. This idea of conversion is understood as the Intellect 'touching' or 'seeing' the One. Plotinus also alludes to the possibility of the soul achieving a mystical union with the One. With this in mind an interesting question arises: what is the relationship between Plotinus' metaphysics and his mystical union? In this book, I will consider the metaphysical system of emanation and conversion in Plotinus and investigate how that doctrine compares with his mystical union.