  Observational surveys for extrasolar planets probe the diverse outcomes of
planet formation and evolution. These surveys measure the frequency of planets
with different masses, sizes, orbital characteristics, and host star
properties. Small planets between the sizes of Earth and Neptune substantially
outnumber Jupiter-sized planets. The survey measurements support the core
accretion model in which planets form by the accumulation of solids and then
gas in protoplanetary disks. The diversity of exoplanetary characteristics
demonstrates that most of the gross features of the Solar system are one
outcome in a continuum of possibilities. The most common class of planetary
system detectable today consists of one or more planets approximately one to
three times Earth's size orbiting within a fraction of the Earth-Sun distance.
