  Several properties of the Solar System, including the wide radial spacing of
the giant planets, can be explained if planets radially migrated by exchanging
orbital energy and momentum with outer disk planetesimals. Neptune's
planetesimal-driven migration, in particular, has a strong advocate in the
dynamical structure of the Kuiper belt. A dynamical instability is thought to
have occurred during the early stages with Jupiter having close encounters with
a Neptune-class planet. As a result of the encounters, Jupiter acquired its
current orbital eccentricity and jumped inward by a fraction of an au, as
required for the survival of the terrestrial planets and from asteroid belt
constraints. Planetary encounters also contributed to capture of Jupiter
Trojans and irregular satellites of the giant planets. Here we discuss the
dynamical evolution of the early Solar System with an eye to determining how
models of planetary migration/instability can be constrained from its present
architecture.
