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The message of this chapter is that the inclusion of siblings in research makes it possible to address important and novel behavioral genetic questions concerning the etiology of individual differences. We used the topic of perceived competence to demonstrate the utility of five types of sibling analyses: 1) univariate sibling analyses which estimate the importance of shared familial influences; 2) nonshared sibling analysis which asks why siblings are so different from one another; 3) developmental sibling analyses which include comparisons of sibling correlations as a function of age; 4) multivariate sibling analyses which investigate the extent to which familial factors that influence a target trait overlap in their effects on other traits; and 5) DF sibling analysis which examines the familial links between the normal and abnormal.