  Over the past several decades, thousands of planets have been discovered
outside of our Solar System. These planets exhibit enormous diversity, and
their large numbers provide a statistical opportunity to place our Solar System
within the broader context of planetary structure, atmospheres, architectures,
formation, and evolution. Meanwhile, the field of exoplanetary science is
rapidly forging onward towards a goal of atmospheric characterization,
inferring surface conditions and interiors, and assessing the potential for
habitability. However, the interpretation of exoplanet data requires the
development and validation of exoplanet models that depend on in-situ data
that, in the foreseeable future, are only obtainable from our Solar System.
Thus, planetary and exoplanetary science would both greatly benefit from a
symbiotic relationship with a two-way flow of information. Here, we describe
the critical lessons and outstanding questions from planetary science, the
study of which are essential for addressing fundamental aspects for a variety
of exoplanetary topics. We outline these lessons and questions for the major
categories of Solar System bodies, including the terrestrial planets, the giant
planets, moons, and minor bodies. We provide a discussion of how many of these
planetary science issues may be translated into exoplanet observables that will
yield critical insight into current and future exoplanet discoveries.
