From the Document: "The Department of Homeland Security (DHS) is statutorily required to develop and implement an automated biometric (i.e., physical characteristics such as fingerprints, face, or irises) entry-exit system for foreign nationals (referred to as 'aliens' in immigration law) traveling into and out of the United States. The goals of this system are to strengthen national security and help enforce immigration law without disrupting the flow of authorized travel and commerce. The biometric entry system is said to be fully operationalized, whereas the biometric exit system is still being implemented."
CRS In Focus, IF11634
Congressional Research Service: https://crsreports.congress.gov/