The theme of henosis is central in Dionysius' doctrine. The originality of the present study consist in the analysing Dionysius' trinitarian theology and in revealing the structure of De Divinis Nominibus in a movement of procession-conversion from the Union to the One. The author subsequently focuses on De Mystica Theologia, comparing the ascension of Moses with the treatises De Vita Mosis and showing how the rising of the negative theology ends in the unio mystica.