This report offers a theoretical approach to the study of family adaptation to stress. Major works pertaining to family theory, research, and stress, published since 1979, are explored as a theoretical framework, and three conclusions are drawn from these sources: (1) Hill's ABCX model of family stress still influences family stress research; (2) the emphasis in family theory and research is shifting from observing outcomes to explaining them; and (3) systems theory allows for the conceptualization of complex family phenomena. Systems theory, which posits circular relationships among events, is discussed in terms of three concepts which provide a theoretical basis for the study of family adaptation to stress: that any event occurring within the system will have an impact upon the entire system; that there are feedback loops, both positive and negative, which either interrupt or escalate the stress cycle; and the concept of morphogenesis, or events which require a change in family rules in order to restore stability to the system. A systemic model of family stress based on Hill's model is then described, and operational definitions of the six constructs included in the theoretical model are discussed: health problems; behavior problems; emote OK (family rules about emotional expression); role flexibility; emote (experienced emotions); and adapt (absence of problems previously present). Methods of measuring each of these constructs are also discussed. Graphic illustrations of Hill's ABCX model and of the systematic revision are appended. (AG)