  Asteroids and comets are remnants from the era of Solar System formation over
4.5 billion years ago, and therefore allow us to address two fundamental
questions in astronomy: what was the nature of our protoplanetary disk, and how
did the process of planetary accretion occur? The objects we see today have
suffered many geophysically-relevant processes in the intervening eons that
have altered their surfaces, interiors, and compositions. In this chapter we
review our understanding of the origins and evolution of these bodies, discuss
the wealth of science returned from spacecraft missions, and motivate important
questions to be addressed in the future.
