This thesis set out to further the understanding of the psychosocial factors that influence the decisions surrounding breastfeeding, when carried out by younger women; including the attitudes of non-pregnant adolescents, pregnant mothers and breastfeeding mothers. Three quantitative studies and one qualitative study were carried out. The latter found that important themes to emerge were: the importance of self-confidence in parenting and breastfeeding, social norms and maintaining a positive attitude. The five young mothers who took part in the qualitative study were a sub-sample of the 57 women who took part in the first quantitative study. This study found that there were differences of self-esteem, attitudes, general self-efficacy and postnatal breastfeeding self-efficacy between the age-groups with the older mothers having higher scores. After childbirth there was a significant drop in breastfeeding self-efficacy scores and this was especially the case for the younger mothers. General self-efficacy and breastfeeding self-efficacy were predictive of the duration of breastfeeding independently of age. Also there was an association between the length of time spent in education and the likelihood of the mothers still breastfeeding at four months. The second quantitative study examined the differences in attitudes between young adults and older adults and found that older adults had more positive attitudes, although they did not differ between men and women. When the 2005 figures are compared with 1981, it is evident that there has been very little increase in attitudes amongst young people and no increase in knowledge. Also there was a lack of education about breastfeeding reported. Therefore the third study was an intervention in schools with 92 girls. This increased the attitudes in the intervention group, but intentions were not increased. Theory of planned behaviour (TPB) variables predicted intention, but whether the girl had been breastfed herself was also found to be a strong predictor of intention. From the results of these studies it is possible to conclude that, in the way they influence breastfeeding behaviour, attitudes and self-efficacy are not stable traits. Rather, they are changed over time by life experiences, body image, and social and cultural factors and can be changed too by health education interventions.