Hate, a simple word, is easily understood by young children. But as a concept, hate is vast, complex, and slippery. The study of hate is not limited to one discipline; it is studied throughout the humanities and social sciences. This paper, which presents a psychological theory of hating, argues that hate is an understudied psychological construct and has particular relevance to justice research. Hate can trigger injustice, and injustice has the capacity to trigger derogation, violence, and hate. Relying on four literatures-justice, psychology, psychoanalysis, and criminal justice-we present a theory of hating that describes the formation, perpetuation, and expression of this influential emotional state. The Intensification Theory of Hating describes hate as a dynamic process that moves from antecedents to emotions, cognitions, morals, and behaviors. Hate, we argue, is not only an emotion; it becomes systemic when interactions among its components unfold over time to intensify hate. We conclude by proposing research approaches and questions that could address hate in psychological and justice research.