Summary: The VPI (Variable Precision Interval) software package is a collection of routines written in C++ (by this author) to support variable precision interval arithmetic. It appears to be the oldest of the various C++ packages, having been used as early as 1988, although it has endured many modifications and enhancements since then. Here, the author discusses its capabilities, flaws, evolution (including the development of a vectorized version for the CRAY-YMP), and a variety of pedagogical and research applications to which the author has put it.