Reporting Efficiently to Proper Officials in Response to Terrorism Act of 2017 or the REPORT Act This bill requires the primary government agency investigating an act of terrorism that occurs in the United States, in collaboration with the Department of Homeland Security (DHS), the Department of Justice (DOJ), the Federal Bureau of Investigation (FBI), and, as appropriate, the National Counterterrorism Center (NCC), to submit to Congress an unclassified report on such act not later than one year after the completion of the investigation. Such required reports may be combined into a quarterly report to Congress. This reporting requirement shall not apply in instances in which DHS, DOJ, the FBI, or the NCC determines that the information required to be reported could jeopardize an ongoing investigation or prosecution, in which case Congress shall be notified of such determination before the first anniversary of the completion of the investigation. Each such report shall include: (1) a statement of the facts of the act of terrorism, (2) an explanation of any gaps in national security that could be addressed to prevent future acts of terrorism, (3) recommendations for additional measures that could be taken to improve homeland security, and (4) a summary of the report for public distribution.