This chapter explores the psychological impact of unmanned weapons systems on military decision making. Just war theory is used as a normative framework to evaluate whether decision making is morally acceptable before, during, and after conflict. We discuss the psychology of decision making at the strategic, operational, and tactical levels, and question whether the novelty of unmanned weapons systems can bias the consideration of ethics during conflict. We provide theoretical hypotheses that describe how the possession of unmanned weapons systems may influence military decisions. We query whether military decision makers have an appropriate level of understanding and expertise in using these systems; importantly when considering the trade-off between short-term tactical advantage and long-term strategic goals, and offer recommendations for research.