We have made the first VLBI synthesis images of the H _ { 2 } O maser emission associated with the central engine of the Seyfert galaxy NGC 1068 .
Emission extends about \pm 300 km s ^ { -1 } from the systemic velocity .
Images with submilliarcsecond angular resolution show that the red-shifted emission lies along an arc to the northwest of the systemic emission .
( The blue-shifted emission has not yet been imaged with VLBI . )
Based on the maser velocities and the relative orientation of the known radio jet , we propose that the maser emission arises on the surface of a nearly edge-on torus , where physical conditions are conducive to maser action .
The visible part of the torus is axially thick , with comparable height and radius .
The velocity field indicates sub-Keplerian differential rotation around a central mass of \sim 1 \times 10 ^ { 7 } M _ { \odot } that lies within a cylindrical radius of about 0.65 pc .
The estimated luminosity of the central engine is about 0.5 of the Eddington limit .
There is no detectable compact radio continuum emission near the proposed center of the torus ( T _ { B } < 5 \times 10 ^ { 6 } K on size scales of \sim 0.1 pc ) , so that the observed flat-spectrum core can not be direct self-absorbed synchrotron radiation .