This thesis describes a program of research which aimed to identify the extent to which couple and stepfamily variables were associated with couple relationship adjustment and stability in stepfamily couples. Two studies were conducted. Study 1 consisted of 63 stepfamily couples who were in a committed relationship (married or cohabiting) and who had earlier taken part in an intervention program. It was hypothesised that positive couple relationship outcomes could be predicted by low couple aggression, high couple negativity, low couple withdrawal, high parenting disagreement, and high dysfunctional parenting over a 5-year period. The results did not support the hypotheses possibly due to low power in the design. In Study 2, 122 stepfamily couples who been living together (married or cohabiting) as a stepfamily were assessed on couple and stepfamily factors, and these were tested for their association with couple relationship adjustment and stability, using both self-report questionnaires and interview data. As predicted, stepfamily factors accounted for variance in couple stability above that accounted for by couple factors. Furthermore, stepfamily factors were associated with couple stability independent of couple adjustment. The influence of stepfamily couple relationship adjustment and stability seem distinctive from first-marriage couples. It was concluded that stepfamily relationship education programs for stepfamilies should address the unique needs of stepfamilies such as parenting education for inexperienced stepparents, the development of positive stepparent-stepchild relationships, and the building of stepfamily cohesion.