  In this review we re-evaluate our observational and theoretical understanding
of the chemical evolution of protoplanetary disks. We discuss how improved
observational capabilities have enabled the detection of numerous molecules
exposing an active disk chemistry that appears to be in disequilibrium. We
outline the primary facets of static and dynamical theoretical chemical models.
Such models have demonstrated that the observed disk chemistry arises from warm
surface layers that are irradiated by X-ray and FUV emission from the central
accreting star. Key emphasis is placed on reviewing areas where disk chemistry
and physics are linked: including the deuterium chemistry, gas temperature
structure, disk viscous evolution (mixing), ionization fraction, and the
beginnings of planet formation.
