1. Significance/background Polygyny is rarely, if ever, included in family planning (FP) messaging in Sub-Saharan Africa, even though the region has the world’s highest rates of polygyny. In West Africa a majority of women will spend some portion of their married life in a polygynous union as a co-wife. Research on polygyny has tended to focus on the influence of polygyny on outcomes such as fertility preferences and rates and contraceptive use, and there is little consensus as to the direction of these relationships. The role played by polygyny in the design and consumption of FP programs has been ignored. For example, the study of spousal communication about FP has been limited to monogamous couples and there is no model for spousal communication within polygynous marriages. This paper will focus on the ways in which – if at all – polygyny is represented by, or addressed in, family planning programs in sub-Saharan Africa. It assesses the presence (or absence) of polygyny in FP messaging and research and argues that polygynous unions are sufficiently different from monogamous unions to warrant audience segmentation in FP programs in areas with high levels of polygyny. 2. Main question/hypothesis This paper aims to assess the place of polygyny in FP messaging in sub-Saharan Africa, and whether a case should be made for segmentation by marriage type (polygynous/monogamous) in FP communication. It sets out three research questions in order to address this aim: i. Do the FP experiences of men and women differ significantly between monogamous and polygynous marriages? ii. How is polygyny represented in FP messaging? iii. What might be the consequences of excluding polygyny from FP program design and implementation? 3. Methodology This paper uses mixed methods including: i. Systematic mapping of the research relating to polygyny and FP in sub-Saharan Africa ii. Review FP visual communication materials (e.g.: JHU Bloomberg School of Public Health Center for Communication Programs Media/Materials Clearinghouse) for evidence pertaining to polygyny in family planning messaging iii. Secondary quantitative analyses of DHS data Our mapping of current literature reveals little consensus on the relationship between polygyny and fertility. While many studies conclude that individual fertility is lower for polygynous than for monogamous women (although polygyny increases fertility at the aggregate level because fewer women remain unmarried) others report that polygynous women have higher fertility than their monogamous counterparts. Polygyny increases individual male fertility. Our analyses of polygyny and its effects on fertility intentions and behaviors, contraceptive use, and husband-wife communication regarding FP consider whether men and women in polygynous unions face situations different from their monogamous counterparts. By comparing results on FP perceptions, intentions and behaviors of polygynous men and women this those in monogamous marriages, we demonstrate how using conventional models of couples’ analysis (i.e. studying monogamous couples) is inappropriate for researching polygynous unions, which should therefore be specifically segmented and targeted in FP messaging. 4. Results/key findings Polygyny is rarely, if ever, included in FP messaging in Sub-Saharan Africa, even in areas with high rates of polygyny. Polygynous marriages differ from monogamous marriages in a number of crucial ways (greater age difference between polygynous spouses, decreased decision-making power for wives, higher fertility preferences for men, competition for a husband’s resources, and lower spousal communication about FP) that have major implications for FP programs. Polygynous marriages may result in higher fertility preferences for women, longer periods of breast-feeding and post-partum abstinence, and decreased likelihood of contraceptive use and increased likelihood that, if used, it would be clandestinely. While formally recognized polygyny is declining, it is often replaced by unofficial forms of polygynous unions (“private polygyny”). Polygyny may be increasingly replaced by private polygyny because polygyny is now often considered less acceptable or is illegal. Many seemingly monogamous marriages are actually adapted forms of polygyny, with unofficial outside wives. Lastly, polygyny seems to have a strong effect on men’s desired number of children, which are considerably greater than those of both polygynous women and monogamous men or women. Desired high fertility is often given as a reason for marrying polygynously. The implication for this kind of marriage decision on family size and for FP programs is significant. 5. Knowledge Using conventional models of couples’ analysis (i.e. studying monogamous couples) may be inappropriate for researching polygynous unions. Polygyny is often disregarded or misrepresented in research, even when studies are carried out in areas with high rates of polygyny. Men and women in polygynous unions have markedly different experiences than do their monogamous counterparts. Ignoring the reality of polygyny in FP communication has implications for the effectiveness of family planning campaigns in parts of Africa with high rates of official and/or unofficial polygyny. We conclude with suggestions of ways that polygyny might be included in FP messaging in Sub-Saharan Africa.