The document discusses different types of family structures including nuclear families, matrifocal families, vertically and horizontally extended families, reconstituted families, single person households, single parent families, polyandry, polygyny, promiscuity, and monogamy. It notes that nuclear families were more common in the 19th century while single person households and couples without children have grown in the 20th century. Certain structures like matrifocal families have been identified among poor communities.