  I review recent results from gravitational microlensing surveys of the Large
Magellanic Cloud. The combined microlensing optical depth of the MACHO and
EROS-1 surveys is tau_LMC = 2.1{+1.3/-0.8}* 10^{-7} which is substantially
larger than the background of tau < 0.5* 10^{-7} from lensing by known stars
but is below the expected microlensing optical depth of tau = 4.7*10^{-7} for a
halo composed entirely of Machos. The simplest interpretation of this result is
that nearly half of the dark halo is composed of Machos with a typical mass of
order 0.5 Msun. These Machos could be old white dwarfs, but it is not obvious
that the generation of stars that preceded these white dwarfs could have gone
undetected. Perhaps, the Machos could be non-baryonic, but there is no
compelling model for the formation of non-baryonic Machos. Therefore, some
authors have tried to develop alternative models which attempt to explain the
LMC microlensing results with non-halo lenses. Many of these models postulate
previously unknown dark stellar populations which contribute significantly to
the total mass of the Galaxy and are therefore simply variations of the dark
matter solution. However, models which postulate an unknown dwarf galaxy along
the line of sight to the LMC or a distortion of the LMC which significantly
enhances the LMC self-lensing optical depth can potentially explain the LMC
lensing results with only a small amount of mass, so these can be regarded as
true non-dark matter solutions to the Macho puzzle. All such models that have
been proposed so far have serious problems, so there is as yet no compelling
alternative to the dark matter interpretation. However, the problem can be
solved observationally with a second generation gravitational microlensing
survey that is significantly more sensitive than current microlensing surveys.
