The relations between personality and behaviour in relationships pose special problems (Auhagen, 1994; Auhagen & Hinde, in press), many of which relate ultimately to the nature of the self (see Chapter 3). We all have a feeling of on-going identity—that we continue to be the same person in different contexts. At the same time we know that we behave differently according to whom we are with. While much of the variance in many individual characteristics can be traced to genetic factors (Goldsmith, 1983; Loehlin, Willerman, & Horn, 1988; Plomin, 1990), personality is shaped by experience, especially in early childhood (Bowlby, 1969/82, 1973, 1980; Plomin, 1990). And while measures of individual characteristics show reasonable temporal continuity, they can be changed by life events (Goodyer, 1990; Paykel, 1983; Wink & Helson, 1993). We must therefore recognise from the start the importance of the dialectical relations between the individuals and their behaviour on the one hand and the relationships with which we are concerned on the other (Frontispiece).