Three studies are proposed that will examine basic issues in the study of individual differences in behavioral style, or temperament, during the first year of life. The questions that these studies will address include: (1) are there observable stabilities in the behavioral style of children during the first year of life of the type assumed by theories of temperament; (2) do methods of aggregation improve the reliability of such observations; (3) do methods of aggregation improve the reliability of parental reports of child temperament; (4) does aggregation of both child observations and parental reports improve the degree of correspondence between them; and (5) are parents accurate direct observers of infant behavioral style. The first study will follow 50 mother-infant dyads from 4 through 12 months of life. Weekly observations of child behavior will be made, and weekly parental reports will be obtained. Analysis will be directed at determining an optimal number of observations necessary to achieve reliability of observation or report using these methods. In study 2, mothers will rate various scales of behavioral style for video records of their own children as well as tapes of standard children that all mothers will rate. Analysis will concentrate on whether mothers in general use a consistent set of norms when reporting to professionals about child temperament. Study 3 will combine the methods developed in studies 1 and 2 to replicate the findings of those studies as well as provide validation for a final parent report instrument developed during the course of this project. Multiple observations of child behavior (the number determined by the results of study 1) will provide the behavioral base for this validation.