This thesis investigated the relationship between postnatal depression (PND) and maternal sensitivity. Part one is a systematic literature review. This review summarizes the evidence regarding the relationship between PND and a number of maternal parenting behaviour constructs, including maternal sensitivity. There seemed to be more evidence of a negative association between PND and some maternal parenting behaviour constructs more than others. Part two describes a cross-sectional study of the relationship between PND and maternal sensitivity in a disadvantaged and high risk sample of 86 mothers. The findings revealed no evidence of an association between PND and maternal sensitivity, though there was some evidence of an association between antenatal depression and sensitivity. Finally, a critical appraisal of the entire research is presented in part three. Therein, reflections are proffered on issues related to the coding of sensitivity, the role for qualitative research in this area as well as further clinical implications and directions for future research. This was a joint thesis undertaken in conjunction with Roberts (2018), whom coded half of the data for sensitivity (please see Appendix A for further details).