United Nations peacekeeping soldiers commit atrocities while deployed despite their mandate to protect civilians from harm. Yet, there is tremendous variation across missions in reported human rights abuses. Why are some missions more susceptible to misconduct than others? To answer this puzzle, we identify three broad sources of influence on peacekeeper behavior: institutions, society, and military culture. Using newly collected data, we find that host-country and contributing-country institutions, particularly press freedoms and rule of law, dramatically decrease violations. Compliance with international humanitarian law also decreases violations, though to a lesser degree than institutions. Societal influences, such as gender norms and income inequality, have virtually no impact on abuses. We illustrate the utility of these findings by generating out-of-sample predictions for hypothetical peacekeeping missions in countries with recent political turmoil.