  Thousands of extrasolar planets have been discovered, and it is clear that
the galactic planetary census draws on a diversity greatly exceeding that
exhibited by the solar system's planets. We review significant landmarks in the
chronology of extrasolar planet detection, and we give an overview of the
varied observational techniques that are brought to bear. We then discuss the
properties of the currently known distribution, using the mass-period diagram
as a guide to delineating hot Jupiters, eccentric giant planets, and a third,
highly populous, category that we term "ungiants", planets having masses less
than 30 Earth masses and orbital periods less than 100 days. We then move to a
discussion of the bulk compositions of the extrasolar planets. We discuss the
long-standing problem of radius anomalies among giant planets, as well as
issues posed by the unexpectedly large range in sizes observed for planets with
masses somewhat greater than Earth's. We discuss the use of transit
observations to probe the atmospheres of extrasolar planets; various
measurements taken during primary transit, secondary eclipse, and through the
full orbital period, can give clues to the atmospheric compositions,
structures, and meteorologies. The extrasolar planet catalog, along with the
details of our solar system and observations of star-forming regions and
protoplanetary disks, provide a backdrop for a discussion of planet formation
in which we review the elements of the favored pictures for how the terrestrial
and giant planets were assembled. We conclude by listing several research
questions that are relevant to the next ten years and beyond.
