The present invention relates to compounds useful as inhibitors of indoleamine 2,3-dioxygenase (IDO). The invention also relates to pharmaceutically acceptable compositions comprising the compounds of this invention； methods of treating of various diseases, disorders, and conditions using the compounds of this invention； processes for preparing the compounds of this invention； intermediates for the preparation of the compounds of this invention； and methods of using the compounds in in vitro applications.. The compounds of this invention have formula I-A； wherein the variables are as defined herein.
