Insecure Attachment Style is increasingly acknowledged as an important developmental risk factor for psychological disorder. However, in adolescence, its association with different types of disorder, intergenerational transmission and continuity of insecurity from infancy require further investigation. The thesis investigated three main themes in mother adolescent-offspring dyads: A) A cross-sectional analysis examining the relationship of insecure Attachment Style and internalising disorder (in both generations) and disorder (in adolescence alone). B) Concurrent investigation of intergenerational transmission of mothers' Attachment Style and disorder to the adolescent offspring. C) Continuity of Attachment Style over time: within an individual (from infancy to adolescence in the younger generation), and trans-generational (from the mothers to the offspring in infancy) and how it affects the adolescent's current functioning. The study utilised an existing sample of non-clinical mother-offspring dyads studied 15 years earlier and newly followed up. New data from 43 mother-adolescent dyads were collected both by questionnaire and interview to determine clinical symptoms and Attachment Style. The Attachment Style Interview was used for the adolescents while the Vulnerable Attachment Style Questionnaire (VASQ) was used for mothers. Previously collected data using the Adult Attachment Interview and the SSP Procedure in infants were also utilised. Findings show that Anxious Attachment Style in the adolescents' was associated with both internalising and Externalising disorder. Avoidant Style (Withdrawn) was not associated with any disorder. In mothers the total VASQ insecurity scale was highly significantly associated with both their depression and trait anxiety (theme A). Mothers' internalising disorder was associated with adolescent disorder, both internalising and Externalising. However, there was no association between mothers' and adolescents' Attachment insecurity, and mother's insecure Attachment Style was unrelated to adolescent disorder (theme B). Finally, there was continuity of insecure Attachment in mothers over the intervening years, but not in adolescents. The results indicate that insecure Attachment Style is a risk factor for psychological disorder at different life stages and it is important to acknowledge this in clinical treatment and interventions in high risk children and families.