Increases in parental cohabitation, separation or divorce, and re-partnering or remarriage have generated an increase in the complexity of family and kinship ties. As a result, many scholars claim that family and kinship have become voluntary, with rights and obligations to be negotiated in the same way as those between friends and neighbors. This essay briefly reviews the demographic trends that have produced complex families and kin, and their projections into the future. It argues that kinship structures arising from stable nuclear family and kin networks provide a template for the organization of more complex family ties. Although a considerable degree of voluntariness can be found in ties among complex families and kin, rights and obligations remain structured in terms of blood and marriage, and are also strongly influenced by periods of coresidence. Guidelines do exist for relationships in complex families and kinship networks, and they can be used to further institutional arrangements that fit the circumstances of increasingly diverse types of families and kin.