The role of risk taking in building trust relations has largely been overlooked in the burgeoning literature on trust in the social sciences; yet it is central to understanding how trust develops. We argue that a series of risk-taking behaviors is indispensable to building a trust relation. We conducted experiments in Japan and the United States to examine the independent and cross-cultural effects of risk taking on trust building. The results of these experiments indicate that the American participants took more risks than did the Japanese, supporting the general claim that Americans are inclined toward risk taking and trust building. Even so, the Americans were no better than the Japanese at improving the level of cooperation. The cumulative results of these experiments imply that risk taking is a critical element in trust building for Americans, but less so for the Japanese. Our results show clearly that it is important to distinguish trusting behavior from cooperation and to measure them separately if we are to study trust and trust building in relation to social cooperation. (Contains 5 figures, 1 table, and 18 footnotes.)