  The physical composition and structure of meteoroids gives us insight into
the formation processes of their parent asteroids and comets. The strength of
and fundamental grain sizes in meteoroids tell us about the environment in
which small solar system bodies formed, and the processes which built up these
basic planetary building blocks. The structure of meteorites can be studied
directly, but the set of objects which survive entry through the atmosphere is
biased toward large, strong objects with slow encounter speeds. Fragile
objects, small objects and objects with high relative speeds are very unlikely
to survive impact with the atmosphere. Objects between 100 microns and 1 meter,
which are not strong enough to survive the ablation process, must be studied by
radar or optical methods.
  Large meteoroids, which produce bright fireballs, are generally studied by
investigating their compressive strength when they fragment, and their strength
can also be inferred indirectly from their end heights.
  Fragmentation in faint meteors can be inferred from interference in radar
observations, or observed directly with high-resolution optical systems. Meteor
light curves, begin heights and time-evolving spectra can also be used to infer
meteoroid structure.
  This paper presents a review of the meteor observation methods currently used
to infer the structure and fragmentation of meteoroids in the millimeter to
meter size range, and the current state of understanding these observations
have given us.
