Comprise correspondence, including series of letters from Ferdinand Freiligrath, Clara Neymann, and Mathilde F. Wendt; correspondence and documents relating to Der Pionier, with many letters relating to his efforts in 1862 to prevent confirmation of Col. L. Blenker as Brig. Gen. in the U.S. Army; manuscripts of his Gedichte and Erlebtes, and other works including poems, lectures, and articles; personal documents; and family papers including those of his father, Joseph Heinzen, and of his wife, Henriette Schiller Heinzen, including the Schiller and Moras family papers. Other correspondents include L. Bamburger, H. von Ende, H. Erichsen, K. Röser, J. A. Sprague, and F. H. Zitz.
Heinzen, a German refugee of 1848-49, was a radical author and lecturer and, from 1854 to 1879, editor of Der Pionier. Correspondence relating to Der Pionier, his efforts to prevent confirmation of Col. Ludwig Blenker as brigadier general in the United States Army, and other matters; manuscripts of his poems, lectures, articles, and other works, including Gedichte and Erlebtes; and family papers of his father, Joseph Heinzen, and his wife, Henriette Schiller Heinzen (Schiller and Moras families). Correspondents include Louis Bamberger, Heinrich von Ende, Hugo Erichsen, Ferdinand Freiligrath, Clara Neymann, Karl Roser, Julia A. Sprague, Mathilde F. Wendt, and Franz Zitz. The papers are in German, French, and English, chiefly in old-style German cursive. Many letters are accompanied by transcriptions, translations, or summaries in English.