  Massive stars disrupt their natal molecular cloud material through radiative
and mechanical feedback processes. These processes have profound effects on the
evolution of interstellar matter in our Galaxy and throughout the Universe,
from the era of vigorous star formation at redshifts of 1-3 to the present day.
The dominant feedback processes can be probed by observations of the
Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive
stars create warm regions of gas and dust in the neutral atomic and molecular
gas. PDR emission provides a unique tool to study in detail the physical and
chemical processes that are relevant for most of the mass in inter- and
circumstellar media including diffuse clouds, proto-planetary disks and
molecular cloud surfaces, globules, planetary nebulae, and star-forming
regions. PDR emission dominates the infrared (IR) spectra of star-forming
galaxies. Most of the Galactic and extragalactic observations obtained with the
James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this
paper we present an Early Release Science program using the MIRI, NIRSpec, and
NIRCam instruments dedicated to the observations of an emblematic and nearby
PDR: the Orion Bar. These early JWST observations will provide template
datasets designed to identify key PDR characteristics in JWST observations.
These data will serve to benchmark PDR models and extend them into the JWST
era. We also present the Science-Enabling products that we will provide to the
community. These template datasets and Science-Enabling products will guide the
preparation of future proposals on star-forming regions in our Galaxy and
beyond and will facilitate data analysis and interpretation of forthcoming JWST
observations.
