For many decades Giacomo Leopardi's Zibaldone di pensieri has been seen as a collection of temporary thoughts and impressions whose final expression is to be found in the published poems (the Canti) and satirical dialogues (the Operette morali). The conceptual consistency of the work was thereby denied, privileging Leopardi the poet over Leopardi the thinker. This book shows that such a perceived lack of coherence is merely illusory. The Zibaldone is drawn together by an intricate web of references centring around topics such as the ambivalent concept of nature; the Heraclitean "union of opposites" (ancients and moderns, poetry and philosophy, reason and imagination); and the tension between the desire for happiness and the impossibility of its realization. Largely unknown to the English-speaking world until its translation in 2013, the Zibaldone is Leopardi's intellectual diary, the place where dialogue with the ancient classical traditions evolves into modern encyclopaedism and what has been described as "thought in movement". It establishes Leopardi as one of the most original and radical thinkers of the nineteenth century.