The study of moral judgement and decision making examines the way predictions made by moral and ethical theories fare in real world settings. Such investigations are carried out using a variety of approaches and methods, such as experiments, modeling, and observational and field studies, in a variety of populations. The current Collection on moral judgments and decision making includes works that represent this variety, while focusing on some common themes, including group morality and the role of affect in moral judgment. The Collection also includes a significant number of studies that made theoretically driven predictions and failed to find support for them. We highlight the importance of such null-results papers, especially in fields that are traditionally governed by theoretical frameworks.The study of moral judgement and decision making examines the way people behave and react to social and moral dilemmas. Moral and ethical theories usually provide the foundation for such efforts, providing important constructs and definitions, and even suggesting hypothetical experimental designs. A good example is the differentiation between deontological and utilitarian basis of moral action selection. Characteristically utilitarian approaches look at the overall benefit of each action, while characteristically deontological approaches set principles, prohibiting some actions regardless of their ultimate outcome. Both approaches provide predictions for moral decisions and use hypothetical scenarios such as personal versus impersonal trolley-type problems to illustrate the different predictions. In recent years researchers have been putting such theories to the test in a variety of experimental designs and populations. Translating theoretical hypotheses and constructs to an experimental paradigm or an operational prediction is not trivial. Participants' individual traits and their cultural and societal context introduces variability and nuances to ethical theories. In addition, the technical need to build a robust and reliable experimental design, which can be evaluated using statistical tools, leads researchers to adopt experimental designs from different fields, such as economics and cognitive psychology.