Objective 1: To examine the influence of maternal depression and/ or anxiety on infant, maternal and dyadic FFSF task performance Objective 2: To investigate the changes in infant and maternal FFSF task performance before and after Cognitive Behavioural Therapy (CBT) treatment of maternal depression / Background: Research suggests that postpartum depression (PPD) and postpartum anxiety (PPA) impact both mothers and their infants, leading to adverse behavioural outcomes across the lifespan. The face-to-face still-face (FFSF) task is a validated observational tool used to measure the quality of mother-infant interactions. This thesis aimed to investigate the differences in responses to the FFSF task between dyads consisting of mothers with PPD and/or PPA and healthy dyads. Another goal was to examine whether PPD treatment could improve mother and infant FFSF outcomes. Methods: A systematic search was performed in PubMed/MEDLINE, EMBASE, CINAHL, PsycINFO and Web of Science. Meta-analyses were conducted to examine the differences in infant, maternal and dyadic FFSF outcomes in mothers with PPD, PPA or comorbid PPD and PPA in comparison to healthy control dyads. Second, we examined whether group cognitive behavioural therapy (CBT) for PPD could help improve infant and maternal FFSF outcomes. A case-control design study was conducted with three different assessment points (i.e., pre-CBT treatment, immediately after CBT and three months post-CBT). Results: Meta-analyses suggested that the infants of mothers with PPD display lower levels of positive affect during the play and reunion phases compared to the infants of healthy non-depressed mothers. Also, mothers with PPD may engage less positively with their infants at the reunion phase, and mother-infant dyads affected by PPD show less positive interactive matching during the play phase compared to healthy control dyads. Finally, object/environment engagement was higher in infants of PPA mothers compared to healthy controls at still-face. Conclusion: The results suggest that mothers with PPD and/or PPD (and their infants) may exhibit different interaction patterns compared to healthy dyads. Also, it appears that the benefits of CBT for maternal PPD may extend to their infants through reductions in maladaptive infant withdrawn behaviours to normal, healthy levels. / Thesis / Master of Science (MSc) / Maternal postpartum depression (PPD) and postpartum anxiety (PPA) are the most common mental health complications of birth. Apart from unfavourable effects PPD and PPA have on mothers, it may also impact the mother-infant relationship, leading to adverse infant outcomes. Given the relatively high prevalence of maternal PPD, PPA, and comorbid PPD and PPA, this thesis aimed to examine the differences in how mothers suffering from PPD and/or PPA and their infants coordinate their behaviour, in comparison to healthy mothers and their infants using a validated observational task (face-to-face still-face [FFSF] task). Another goal of this thesis was to investigate whether the benefits of maternal treatment for PPD with cognitive behavioural therapy may extend to infants and improve mother, as well as infant behaviour. These investigations may provide new insights on how maternal PPD and/or PPA affects mother-infant interactions, and consequently, infant socio-emotional development.