We conducted this audit to determine the effectiveness and cost of the Unmanned Aircraft System program, in which U.S. Customs and Border Protection ( CBP) has invested significant funds. Although CBP’s Unmanned Aircraft System program contributes to border security, after 8 years, CBP cannot prove that the program is effective because it has not developed performance measures. The program has also not achieved the expected results. Specifically, the unmanned aircraft are not meeting flight hour goals, and we found little or no evidence CBP has met its program expectations. We estimate it costs $12,255 per flight hour to operate the program; CBP’s calculation of $2,468 per flight hour does not include all operating costs. By not recognizing all operating costs, CBP cannot accurately assess the program’s cost effectiveness or make informed decisions about program expansion. In addition, Congress and the public may be unaware of all the resources committed to the program. As a result, CBP has invested significant funds in a program that has not achieved the expected results, and it cannot demonstrate how much the program has improved border security. The $443 million CBP plans to spend on program expansion could be put to better use by investing in alternatives.