The present study is an investigation into a little studied aspect of the thought of Thomas Aquinas, namely, his view of the nature and experience of beauty. Aquinas has defined beauty, provisionally, as “that which pleases when seen.” This study is structured around the three key components of the definition: (1) the things themselves, including the formal constituents of beauty found in things, (2) Aquinas' philosophical psychology of perception, and (3) desire and pleasure. My aim is to examine the connection between Aquinas' account of desire and pleasure and their relation to his moral thinking, on the one hand, and his account of aesthetic pleasure and its implications for his moral thinking, on the other. From this discussion, as well as from a careful examination of select texts from his commentary on Dionysius' De divinis nominibus, I shall argue that Aquinas holds spiritual or moral beauty to be his primary aesthetic concern, and only derivatively does he concern himself with natural or physical beauty. The study concludes with a comparison between the commentaries of Aquinas and his mentor, Albertus Magnus, highlighting the great similarity between the two accounts as well as what appears to be a significant dependence of Aquinas's thought upon that of his teacher with respect to this subject. This study also highlights one area, namely beauty, in which Aquinas' thought is significantly more Platonic than Aristotelian.