The purpose of this review is to establish a groundwork for building a more comprehensive conceptual framework within which various aspects of sibling relations and factor related to sibling behaviors con be explained and integrated. Descriptions of the trends and shifts in sibling studies are made in terms of their themes, variables, basic perceptions and general approaches, and analyzes of current state of sibling researches are made with relation to the conceptual aspects of the studies, namely, their standpoints on the issues of sibling variations, the sources of variations, and basic units of analysis, their reliance or emphasis on different methods, and their interests in the mediation processes. It is recognized that research variables have been successively differentiated and used in diversified manners and family ecology and systems theory viewpoints have been incorporated into the understanding of sibling relations. A triad in its full meaning, rather than a dyad or a partial trial, is proposed as a unit of analysis in order for the researchers to be able to examine and describe the true interactional aspects of family relations involving sibling relations. The concepts of coexistence and interaction are proposed as key concepts os that the inconsistencies in findings, differing viewpoints, contradicting conceptions , and contrasting approaches can be interpreted and integrated into a unified system of theories on siblings. The coexistence of similarities and differences in reality. the inevitability of interaction between individual variables and environmental variables and between within-family environmental factors and our-of-family environmental factors, and the need for the joint use of intrafamilial and extrafamilial approach are acknowledged. Attention is also drawn to the mechanism characteristics and the directionality of the mediating processes of mediating variables between a variable and its effects.