This volume presents the first edition, along with an English translation, of a Sanskrit work of perhaps the seventh century surviving in a single ninth-century Nepalese witness: the Ni_v_samukhatattvasa_hit_. It would be difficult to exaggerate the usefulness of this primary source for the history of the _aiva religions. Ostensibly an introduction to the Ni_v_samukhatattvasa_hit_, it purports to sketch the religious context in which the Mantram_rga emerged. In so doing, it provides invaluable help in mapping the contours of the relations between four different traditions of early _aivism, namely: 1) that of the P_?c_rthika P__upatas, 2) that of the L_kulas (here lok_t_ta), 3) the the Mantram_rga and 4) pre-Mantram_rga “lay” practices. The work is bracketed by a detailed introduction and an appendix presenting material borrowed into the _ivadharmasa_graha.