Works of art are frequently called "interesting", and the wider grammar of interestingness - "mysterious", "complex", “enlightening”, etc. - is pervasive in contemporary writings about art. Contemporary art has intertwined itself with a form of philosophical discourse, self-reflexive and critical. Moreover, a tradition of philosophers, artists and art critics have, at least since the pre-Kantian development of aesthetics, repeatedly asserted the importance of the interesting for the work of art. For these reasons, it seems that the interesting, rather than, say, beauty, is the central value of art. But how should we understand this centrality thesis? And what is it to be interesting? From a broader perspective, the interesting, as well as its psychological counterpart interest, are relevant beyond and independently of aesthetical contexts. Today, interest is a hot topic both in contemporary epistemology and empirical psychology. The input from the corresponding literatures and further philosophical considerations coming from the philosophy of mind and metaphysics of value, help clarify the concept of the interesting and buttress a general view of the property of being interesting as the value of the potential for one's cognitive improvement. These analyses provide a more solid ground for the further investigation into how the interesting is ascribed to art. The description of numerous art works shows how the category is diversely implicated in their structure, and how important art-critical notions can be traced back to it. This contributes to an understanding of the relation between interestingness and aesthetic value, and further illuminates the role interest has in the experience of art. This work has been awarded with the Humbert Prize by the University of Geneva (2019).