  Protoplanetary disks composed of dust and gas are ubiquitous around young
stars and are commonly recognized as nurseries of planetary systems. Their
lifetime, appearance, and structure are determined by an interplay between
stellar radiation, gravity, thermal pressure, magnetic field, gas viscosity,
turbulence, and rotation. Molecules and dust serve as major heating and cooling
agents in disks. Dust grains dominate the disk opacities, reprocess most of the
stellar radiation, and shield molecules from ionizing UV/X-ray photons. Disks
also dynamically evolve by building up planetary systems which drastically
change their gas and dust density structures. Over the past decade significant
progress has been achieved in our understanding of disk chemical composition
thanks to the upgrade or advent of new millimeter/Infrared facilities (SMA,
PdBI, CARMA, Herschel, e-VLA, ALMA). Some major breakthroughs in our
comprehension of the disk physics and chemistry have been done since PPV. This
review will present and discuss the impact of such improvements on our
understanding of the disk physical structure and chemical composition.
