Risk-factor research refers to the study of antecedent conditions and subsequent outcomes and the ways in which these are interrelated. The research encompasses a broad range of questions and research strategies. The paper discusses the characteristics and contributions of risk-factor research in the context of developmental psychopathology. The ways in which causal paths are conceptualized, the capacity to integrate multiple influences, and applications that can be derived from the findings are discussed. The progression of research is illustrated in relation to key concepts (correlate, risk factor, marker, causal risk factor) that reflect varied levels of understanding antecedent-outcome relations. The identification of causal relations, progressions, and paths over the course of development and the interplay of theory, research, and application are illustrated and discussed.