The Formation of Star and Planetary Systems: New Results from Spitzer
  Protoplanetary disks are thought to be the birth places of planetary systems.
The formation and the subsequent evolution of protoplanetary disks are
regulated by the star formation process, which begins with the collapse of a
cloud core to form a central protostar surrounded by a disk and an overlying
envelope. In the protostellar phase, most of the envelope material is
transferred onto the star through the disk during episodic, high accretion
events. The initial conditions for planet formation in protoplanetary disks are
likely set by the details of these processes. In this contribution, I will
review some of the new observational results from Spitzer on protostellar
evolution and the structure and evolution of protoplanetary disks surrounding
young stars in the nearby star forming regions. The implications of these
results for planet formation and eventual disk dissipation are discussed.
