This Element introduces a new conceptualization of policy experiments. Beyond their mainstream understanding as randomized trials, policy experiments are seen as speculative instances for testing innovative policy instruments to address public concerns. Drawing on Science and Technology Studies, this conception of policy experiments comprises four interrelated processes. First, there is an encounter with a charismatic foreign policy instrument, generating imaginaries of future success. Second, a local issue is problematized, presenting the instrument as its ultimate solution. Third, an experimental mesocosm is assembled to test this problematization empirically. Finally, evaluations of this test are conducted, usually leading to further experiments. The book exemplifies these processes with case studies from Chile, a world leader in policy experimentation in the last decades. The ongoing troubles of public governance worldwide prompt us to conclude by arguing for careful modes of policy experimentation, more tentative, ethical, and inclusive forms of acting in our fragile worlds.