  The ``Homunculus'' nebula around Eta Carinae is one of our most valuable
tools for understanding the extreme nature of episodic pre-supernova mass loss
in the most massive stars, perhaps even more valuable than the historical light
curve of eta Car. As a young nebula that is still in free expansion, it bears
the imprint of its ejection physics, making it a prototype for understanding
the bipolar mass loss that is so common in astrophysics. The high mass and
kinetic energy of the nebula provide a sobering example of the extreme nature
of stellar eruptions in massive stars near the Eddington limit. The historical
ejection event was observed, and current parameters are easily measured due to
its impressive flux at all wavelengths, so the Homunculus is also a unique
laboratory for studying rapid dust formation and molecular chemistry, unusual
ISM abundances, and spectroscopy of dense gas. Since it is relatively nearby
and bright and is expanding rapidly, its 3-D geometry, kinematics, and detailed
structure can be measured accurately, providing unusually good quantitative
constraints on the physics that created these structures. In this chapter I
review the considerable recent history of observational and theoretical study
of the Homunculus nebula, and I provide an up-to-date summary of our current
understanding, as well as areas that need work.
