We determined that U.S. Customs and Border Protection (CBP) IT systems and infrastructure did not fully support its border security objective of preventing the entry of inadmissible aliens to the country. The slow performance of a critical system used for pre-screening travelers reduced Office of Field Operations officers’ ability to identify any passengers who may pose concerns, including national security threats. Further, incoming passenger screening at U.S. international airports was hampered by system outages that created passenger delays and public safety risks. IT systems and infrastructure also did not fully support Border Patrol and Air and Marine Operations border security activities between ports of entry. Poor systems performance and network instability resulted in processing backlogs and agents’ inability to meet deadlines for submitting potential criminal alien prosecution cases. Also, network outages hindered air and marine surveillance operations, reducing the situational awareness needed to detect inadmissible aliens and cargo approaching U.S. borders. CBP has not yet addressed these long-standing IT systems and infrastructure challenges, due in part to ongoing budget constraints. We recommended that CBP take steps to address passenger screening and border security IT systems and infrastructure challenges. We made seven recommendations and CBP concurred with all seven of our recommendations.