This paper outlines a unified scenario for Solar System formation consistent with astrophysical constraints. Jupiter's core could have grown by runaway accretion of planetesimals to a mass sufficient to initiate rapid accretion of gas in times of order of 5 x 10 5−10 6 years, provided the surface density of solids in its accretion zone was at least 5–10 times greater than that required by minimum mass models of the protoplanetary disk. After Jupiter had accreted large amounts of nebular gas, it could have gravitationally scattered the planetesimals remaining nearby into orbits which led to escape from the Solar System. Most of the planetesimals in the Mars-asteroids accretion zone could have been perturbed into Jupiter-crossing orbits by resonances with Jupiter and/or interactions with bodies scattered inwards from Jupiter's accretion zone; such Jupiter-crossing orbits would have subsequently led to ejection from the Solar System. However, removal of excess mass from sunward of 1 AU would have been much more difficult. The inner planets and the asteroids can be accounted for in this picture if the surface density of the solar nebula was relatively uniform (decreasing no more rapidly than r − 1 2 ) out to Jupiter's orbit. The total mass of the protoplanetary disk could have been less than one-tenth of a solar mass provided the surface density dropped off more steeply than r −1 beyond the orbit of Saturn. The outer regions of the nebula would still have contained enough solid matter to explain the growth of Uranus and Neptune in 5 x 10 6−10 8 years, together with the coincident ejection of comets to the Oort cloud. The formation of such a protoplanetary disk requires significant transport of mass and angular momentum, and is consistent with viscous accretion disk models of the solar nebula.