  The basic physical properties of MgB$_2$ have been well established over the
past two years of intensive research. At this point there is a general
consensus about the values for the isotope shift, critical fields, most of the
salient length scales, and general anisotropies. In this paper we will review
the determination of these parameters and set the stage for further, more
detailed discussions of specific aspects of the physics of MgB$_2$.
