The present invention relates to pyrazinecompounds useful as inhibitors of ATR protein kinase.The invention also relates to pharmaceutically acceptablecompositions comprising the compounds of this invention；methods of treating of various diseases, disorders, andconditions using the compounds of this invention；pro-cesses for preparing the compounds of this invention；in-termediates for the preparation of the compounds of thisinvention； and methods of using the compounds in in vitroapplications, such as the study of kinases in biological andpathological phenomena； the study of intracellular signaltransduction pathways mediated by such kinases； and thecomparative evaluation of new kinase inhibitors. Thecom-pounds of this invention have formula (I):wherein thevariables are as defined herein.
