The primary themes in the poetry of Walt Whitman include individualism, democracy, and the beauty of the natural world. His seminal work, "Leaves of Grass," celebrates the human experience and the interconnectedness of all life. Whitman emphasizes the importance of self-expression and personal freedom, capturing the essence of American identity during the 19th century. He explores the themes of love, spirituality, and the sublime, often employing free verse to break traditional poetic forms. His innovative style and inclusive vision have left a lasting impact on American poetry.