Postnatal depression (PND) is an episode of major depression which occurs within the postnatal period. It has major implications for maternal wellbeing, the mother-infant relationship and child development. Whilst there is considerable evidence demonstrating the impact of PND on parenting, there has been limited focus on parenting as an intervention target. Therefore, the foremost aim of this thesis was to assess the efficacy and acceptability of the Baby Positive Parenting Programme (Baby Triple P) in women with Postnatal Depression. In Chapter 1 a broad overview of the PND treatment literature is undertaken. The treatments represent a range including anti-depressant medication, antenatal group interventions, psychoeducation, cognitive behaviour therapy (CBT), interpersonal psychotherapy (IPT), interventions which focus on the mother-infant relationship and baby massage. Chapter 1 highlights the poverty of interventions focusing on parenting as well as limited assessment of dyadic and child developmental outcomes. Therefore, a systematic review in Chapter 2 sought to evaluate the quality and efficacy of treatments which did include the aforementioned outcomes. Having identified the little attention to parenting within the context of PND, Chapter 3 outlines the rationale for targeting parenting in PND and introduces the Triple P Positive Parenting Programme, its evidence base and details Baby Triple P. Self-regulation is also introduced as a possible mechanism for explaining the improvements and maintenance associated with Triple P programmes. Since there is no measure to assess self-regulation, one was designed for the purpose of this study. Chapter 4 presents the methodology for the two aforementioned empirical papers. Chapter 5 presents a Factor Analysis (FA) and psychometric properties of the Brief Parenting Beliefs Scale-baby version, designed to measure self-regulation in new parents. The result was a three-factor, brief reliable measure of self-regulation. Chapter 6 presents the findings from the pilot randomised controlled trial (RCT) of Baby Triple P, compared with treatment as usual (TAU) in a sample of women with PND. Twenty-seven women and their infants (under 12 months) from primary care services in Greater Manchester, UK, were randomised to either receive the eight-session Baby Triple P programme in addition to TAU or to TAU only. Participants were assessed prior to randomisation at Baseline (Time 1), post-treatment (eight weeks for TAU) (Time 2) and three-month follow-up (Time 3). Self-report measures were used to compare groups, including symptoms of depression, happiness, the parenting experience, subjective bonding and self-regulation. An assessor-rated observational measure of mother-infant interaction, the Care Index, and a measure of intervention acceptability were also included. Significant improvements from baseline to post-treatment and baseline to three-month follow-up were found across both Baby Triple P and TAU conditions. However, the present study failed to demonstrate an additive effect of Baby Triple P. Despite the non-significant findings Baby Triple P was found to be highly acceptable to women with PND.Reasons for the non-significant findings are explored. The final Chapter (7) is a general discussion summarising the preceding chapters and provides a critical analysis of the pilot RCT of Baby Triple P.