The telescope, camera, and data management system are designed and built by the LSST Project Team, which is responsible for producing the facility but not for the scientific analysis of the data, which will be made public to the US and Chilean communities and some international partners. Hence, the Project Team is not a scientific collaboration in the usual sense, and the LSST can be more properly viewed as a “facility”, designed to provide data products, than as an “experiment”, designed to carry out specific scientific investigations. In 2008, eleven separate quasi-independent science collaborations were formed to focus on a broad range of topics in astronomy and cosmology that the LSST could address. They were largely responsible for authoring the LSST Science Book \cite{2009arXiv0912.0201L}, which was released in 2009. While these collaborations have been productive, and have provided invaluable service to the LSST Project over the past few years, they have not been formally organized to investigate instruments responses and systematics to their full details, to take part to the integration and tests of the instruments, notably the camera, or to prepare and implement the necessary large-scale analyses chains that go beyond the production of calibrated images and their stacking. All of these activities require an extensive, coordinated research effort well in advance of the onset of data taking. To address that need, the LSST DESC has been created in 2012, in order to develop a high-level plan for the study of dark energy with LSST data \cite{2012arXiv1211.0310L}. This will include the development and optimization of a complete set of dark energy analyses that will be performed with the data, the detailed study of systematic issues that may compromise those analyses, the clarification of the sensitivity of those analyses to various technical aspects of the LSST system design, the generation and refinement of simulations and other tools required to validate the analyses, and the identification and assembly of the computational resources to support such investigations both before and after the onset of data taking. In consequence, the extraction and use with LSST data of the five standard cosmological probes – weak and strong lensing, large scale structures (including baryon acoustic oscillations), clusters, and supernovae – falls naturally within the scope of the DESC.