In late 18th-century Italy, the young baron Cosimo breaks with his family and leaves their home to live in the trees. He never comes down. Making his way through the treetops, he finds no need to set foot on the ground, and he ultimately leaves the trees by way of the sky.

One central theme in this story is the conflict between the individual and society. The physical separation that Cosimo instigates stands for the emotional and intellectual alienation that he feels, most immediately from his family and more generally from society at large.

A related theme is the authenticity of nature versus the artifice of society. Although Italo Calvino was writing in the mid-20th century, he aligns his protagonist within the romantic philosophers of the French Enlightenment, especially Henri Rousseau, in supporting immediate sensory apprehension. Direct experience of the material world is presented as superior, in Cosimo’s view, to the mediated, distorted perceptions imposed by society, including formal schooling. The superiority of the senses over reason is not shown to be absolute, however. Cosimo manages to become quite worldly, educating himself from books and correspondence. The falsity of society is further expressed through the true nobility—as in Rousseau’s “noble savage”—of morally appropriate behavior, which is portrayed as superior to the social hierarchy symbolized by Cosimo’s noble family.

The overall form of the book, as an imaginative parable, expresses an underlying theme of Calvino’s belief in the inadequacy of realism to convey ideas accurately, as well as his move toward fantasy as a primary mode of literary expression.