  The James Webb Space Telescope (JWST) presents the opportunity to transform
our understanding of planets and the origins of life by revealing the
atmospheric compositions, structures, and dynamics of transiting exoplanets in
unprecedented detail. However, the high-precision, time-series observations
required for such investigations have unique technical challenges, and prior
experience with other facilities indicates that there will be a steep learning
curve when JWST becomes operational. In this paper we describe the science
objectives and detailed plans of the Transiting Exoplanet Community Early
Release Science (ERS) Program, which is a recently approved program for JWST
observations early in Cycle 1. The goal of this project, for which the obtained
data will have no exclusive access period, is to accelerate the acquisition and
diffusion of technical expertise for transiting exoplanet observations with
JWST, while also providing a compelling set of representative datasets that
will enable immediate scientific breakthroughs. The Transiting Exoplanet
Community ERS Program will exercise the time-series modes of all four JWST
instruments that have been identified as the consensus highest priorities,
observe the full suite of transiting planet characterization geometries
(transits, eclipses, and phase curves), and target planets with host stars that
span an illustrative range of brightnesses. The observations in this program
were defined through an inclusive and transparent process that had
participation from JWST instrument experts and international leaders in
transiting exoplanet studies. Community engagement in the project will be
centered on a two-phase Data Challenge that culminates with the delivery of
planetary spectra, time-series instrument performance reports, and open-source
data analysis toolkits in time to inform the agenda for Cycle 2 of the JWST
mission.
