Isaac (Isaak) Hirsch Weiss, also Eisik Hirsch Weiss (Hebrew: יצחק הירש ווייס) (February 9, 1815 – June 1, 1905), was an Austrian Talmudist and historian of literature born at Groß Meseritsch, Habsburg Moravia.
After having received elementary instruction in Hebrew and Talmud in various chadorim of his native town, he entered, at the age of eight, the yeshiva of Moses Aaron Tichler (founded at Velké Meziříčí in 1822), where he studied Talmud for 5 years. He then studied at home under a tutor, and later in the yeshiva of Trebitsch, Moravia, under Ḥayyim Joseph Pollak, and in that of Eisenstadt, Hungary under Isaac Moses Perles, returning to his home town in 1837.
From the early age at which Weiss began to study Talmud and rabbinics it may be deduced that he was endowed with remarkable ability. He felt a keen desire for the pursuit of the secular sciences also, of which he was deprived in his youth, although he had been instructed in German by his private tutor. In some of the yeshibot which he attended instruction was given also in the Hebrew language and grammar, but that did not satisfy Weiss. It was for this reason that he changed from one yeshibah to another, hoping that he would ultimately find one in which his desire for learning would be satisfied. Influenced by Nachman Krochmal, by Rapoport, and by Leopold Zunz's Gottesdienstliche Vorträge, Weiss devoted part of his time to the study of religious philosophy. Talmudic studies, however, occupied the greater part of his time, and during the years that he spent in his parents' home he wrote several pamphlets containing novellæ on Talmudic tractates, as well as on the Shulḥan 'Aruk, Yoreh De'ah and Ḥoshen Mishpaṭ. He also kept up a correspondence with many distinguished rabbis, particularly Joseph Saul Nathanson, and contributed to Stern's Kokebe Yiẓḥaḳ and to Kobak's Jeschurun. To the former he contributed articles on general subjects, as well as verses and a number of biographies, among which that of Rab (Abba Arika) deserves special notice. In the Jeschurun he published several articles on the origin of prayer.