  Axion physics is briefly reviewed. Constraints from laboratory searches,
astrophysics and cosmology require the axion mass to be in the range $10^{-6}
\lesssim m_a < 3\cdot 10^{-3}$eV. Near the lower end of this range, axions are
all or a major component of the cold dark matter of the universe. The late
infall of axions, and of any other cold dark matter particles, onto our galaxy
produces streams and caustics in its halo. The outer caustics are topological
spheres whereas the inner caustics are rings. The self-similar model of
galactic halo formation predicts that the caustic ring radii $a_n$ obey the
approximate law $a_n \sim 1/n$. Evidence for this law has been found in a
statistical study of 32 extended and well-measured external galactic rotation
curves, and in the existence and distribution of sharp rises in the Milky Way
rotation curve. Moreover, a triangular feature in the IRAS map of the Galactic
plane is consistent with the imprint of a ring caustic upon the baryonic
matter. Its position coincides with a rise in the rotation curve, the one
nearest to us. These observations imply that the dark matter in our
neighborhood is dominated by a single flow. Estimates of that flow's density
and velocity vector are given.
