This report describes an approach developed to elicit from experts ideas for technology-based challenges that the U.S. Joint Force could confront in the year 2040, as well as results from employing this approach with internal RAND Corporation experts. The approach begins with conducting and qualitatively analyzing a set of exploratory interviews with experts, which in turn informs an open-ended survey to nominate challenges and a close-ended survey to evaluate those challenges. Applying this approach with RAND experts generated 20 challenges. Evaluation of those challenges produced three general clusters: a top cluster with nine challenges that experts believed need urgent science and technology (S & T) investments, should be a major national defense priority, might have impacts with severe consequences, and overall were higher risk to the U.S. Department of Defense (DoD) and the United States; a middle cluster with seven challenges that experts believed might have impacts with severe consequences but did not significantly need urgent S & T investment or need to be a major defense national priority; and a bottom cluster with four challenges that experts did not believe had significance across the dimensions the authors measured.