W.B. Yeats' works are defined by elements of mythology, nationalism, and a deep exploration of spirituality. He often utilized themes from Ireland's folklore, intertwining them with personal experiences to reflect his cultural identity. Yeats's poetry showcases a progression from romanticism to a more modernist approach, characterized by musicality and rich imagery. His engagement with the occult and ideas of theosophy also contribute to the uniqueness of his work, revealing a quest for deeper truths beyond the physical world.