  The center of our Galaxy hosts the best constrained supermassive black hole
in the universe, Sagittarius A* (Sgr A*). Its mass and distance have been
accurately determined from stellar orbits and proper motion studies,
respectively, and its high-frequency radio, and highly variable near-infrared
and X-ray emission originate from within a few Schwarzschild radii of the event
horizon. The theory of general relativity (GR) predicts the appearance of a
black hole shadow, which is a lensed image of the event horizon. This shadow
can be resolved by very long baseline radio interferometry and test basic
predictions of GR and alternatives thereof. In this paper we review our current
understanding of the physical properties of Sgr A*, with a particular emphasis
on the radio properties, the black hole shadow, and models for the emission and
appearance of the source. We argue that the Galactic Center holds enormous
potential for experimental tests of black hole accretion and theories of
gravitation in their strong limits.
