Herzen's Letters offers readers a biographical narrative based on translated and annotated correspondence written by and to Alexander Herzen (1812–1870), one of the most consequential figures in the run-up to the Russian Revolution who has been an inspiration to dissidents fighting authoritarianism and imperialism ever since. Kathleen Parthé has selected the most significant epistolary material from over a dozen volumes, interweaving letters with commentary to provide context on the time of composition. Parthé also provides excerpts from key Herzen writings mentioned in his letters that are not widely available in translation.

While some letters are presented whole, in most cases Parthé selected excerpts that illuminate Herzen's ideas, opinions, and plans, as well as his stylistic gifts. Herzen enjoyed spirited debate, and Herzen's Letters includes the voices of his famous contemporaries, including Mikhail Bakunin, Ivan Turgenev, Lev Tolstoy, and others. In brief introductory essays to the six sections Parthé sketches life events, publications, and settings, as Herzen moved from Moscow to the Urals, Petersburg, Novgorod, the European continent, and England, before returning to the continent for his final years.