Ahron Marcus was a scholar and writer on Kabbalah and Hasidism. Marcus was born and educated in Hamburg, studied at the yeshivah of Boskovice (Moravia) but also acquired a wider philosophical education. In 1861 he left for Cracow where he joined the Hasidim. Between 1862 and 1866 he made several long visits to the hasidic rabbi of Radomsk, Solomon Rabinowicz. He later maintained close relations with many hasidic leaders in Poland and Galicia. A major part of his literary work (mainly in German but with a small amount in Hebrew) was devoted to the defense of Hasidism and an explanation of hasidic doctrines and Kabbalah. His work testifies to great erudition, but has proved unacceptable by the current standards of modern critical scholarship. In his work he defended traditional Judaism against modern Bible criticism and scientific materialism. At the same time, he tried to find confirmation for new insights in philosophy and science in Jewish religious literature, particularly in the writings of Hayyim b. Moses Attar, M. H. Luzzatto, and of Habad Hasidism. Marcus was one of the few Orthodox Jews in Germany who totally adopted Hasidism in theory and practice. He published: Hartmanns inductive Philosophie des Unbewussten im Chassidismus (2 pts., 1889–90); Der Chassidismus (under the pseudonym Verus, 1901, 19273); Barsilai, Sprache als Schrift der Psyche (1905); an edition of Jacob of MarvIge's responsa She'elot u-Teshuvot min-ha-Shamayim with a commentary Keset ha-Sofer, 1895, 19572); Keset ha-Sofer (Bible annotations, largely in Ms., 1912); and Juedische Chronologie (vol. 1, posthumously, 1935). From 1898 to 1899 Marcus edited Krakauer Juedische Zeitung, a paper he published as a vehicle for his ideas. He became an supporter of Theodor Herzl and his Judenstaat, thus becoming one of the pioneers of religious Zionism, though later he turned toward the anti-Zionist Agudat Israel.