  The hundreds of exoplanets that have been discovered in the past two decades
offer a new perspective on planetary structure. Instead of being the archetypal
examples of planets, those of our Solar System are merely possible outcomes of
planetary system formation and evolution, and conceivably not even terribly
common outcomes (although this remains an open question). Here, we review the
diverse range of interior structures that are known to, and speculated to,
exist in exoplanetary systems -- from mostly degenerate objects that are more
than 10 times as massive as Jupiter, to intermediate-mass Neptune-like objects
with large cores and moderate hydrogen/helium envelopes, to rocky objects with
roughly the mass of the Earth.
