  We report on a significantly improved determination of the physical orbit of
the double-lined spectroscopic binary system 12 Boo. We have a 12 Boo
interferometry dataset spanning six years with the Palomar Testbed
Interferometer, a smaller amount of data from the Navy Prototype Optical
Interferometer, and a radial velocity dataset spanning 14 years from the
Harvard-Smithsonian Center for Astrophysics. We have updated the 12 Boo
physical orbit model with our expanded interferometric and radial velocity
datasets. The revised orbit is in good agreement with previous results, and the
physical parameters implied by a combined fit to our visibility and radial
velocity data result in precise component masses and luminosities. In
particular, the orbital parallax of the system is determined to be 27.74 $\pm$
0.15 mas, and masses of the two components are determined to be 1.4160 $\pm$
0.0049 M$_{\sun}$ and 1.3740 $\pm$ 0.0045 M$_{\sun}$, respectively. Based on
theoretical models we can estimate a system age of approximately 3.2 Gyr.
Comparisons with stellar models suggest that the 12 Boo primary may be just
entering the Hertzsprung gap, but that conclusion is highly dependent on
details of the models. Such a dynamic evolutionary state makes the 12 Boo
system a unique and important test for stellar models.
