The proliferation of divorce and remarriage over the last few decades has produced a sharp increase in the prevalence of stepfamilies, a family form famously labeled by Cherlin (1978) as an "incomplete institution" for its ambiguous set of role expectations. Although the large majority of investigations into stepfamilies and step-relations has understandably focused on the consequences of family disruption and reformation for the well-being of parents and children at early stages of the family life cycle (Sweeney, 2010), the potential implications for mature families are equally profound. This is particularly relevant to those individuals who experienced the divorce revolution of the late 20th century and who are now entering their later years in complex families with various configurations of step- and biological relationships (Cherlin, 2010). Consequently, it behooves scholars to examine how mature adults and their adult children negotiate relationships in stepfamilies, particularly as older parents confront the challenges and vulnerabilities of midlife and beyond. This special section brings together eight articles from the Netherlands, Germany, and the United States to address issues relevant to the functioning of mature step-relationships and their implications for the well-being of older stepparents.The empirical literature generally reveals adverse effects of parental divorce and stepfamily formation on intergenerational relationships in adulthood, raising concerns about the adequacy of informal support and care available to repartnered elderly parents (Pezzin, Poliak, & Schone, 2008; Ryan, Smith, Antonucci, & Jackson, 2012; Silverstein & Giarrusso, 2010). Evidence is accumulating that the legacy of divorce and remarriage has a long reach, straining intergenerational relationships and suppressing the support that divorced parents, stepparents, and remarried biological parents might expect from their children in later life (Aquilino, 2005; Shapiro, 2003). Indeed, an emerging consensus is that mid- to late life stepfamilies are developing in new and uncharted ways that require further investigation (Ganong & Coleman, 2012).The articles in this section investigate a variety of intergenerational outcomes in mature stepfamilies (emotional closeness, relationship strength, living arrangements, geographic propinquity, in-person contact, and inclusion in personal networks) and the impact of stepfamily membership on the well-being of older parents (mortality and institutionalization; depression and caregiving burden). Three overlapping conceptual themes are represented by the articles, each with key implications for aging stepfamilies: (a) negotiation of boundary ambiguity, (b) intergenerational resource exchange, and (c) filial norms and expectations.The dilemma of boundary ambiguity is based on uncertainties in the role expectations of partners in step-relationships. Clear guidelines for behavior are often absent, leading to attenuation in the strength of step-relationships and an increase in their fragility. Suanet, van der Pas, and van Tilburg (2013) provided evidence that the boundary dividing biological and steprelationships has blurred over 17 years. A cohort comparison reveals that mature stepparents are more inclusive in considering stepchildren as members of their close personal networks than they were in the past. This suggests that role uncertainties may be waning, because steprelationships in more contemporary cohorts of parents are less likely to be relegated to the periphery of family life.Boundary ambiguity is extended to new family forms in the article by de Jong Gierveld and Merz (2013), who studied intergenerational relations of repartnered parents in livingapart-together (LAT) relationships (defined as marriagelike relationships whereby partners maintain separate residences). The authors found that adult children who resist accepting their parent's new partner tend to prefer an LAT arrangement because it preserves geographic boundaries, without which active conflict might emerge with the new partner. …