Niyoga is a type of practice for progeny (children) to continue the family lineage. Through niyoga a wife or a widow was allowed to bring forth a son through co-habitation with an appointed male. This arrangement was made at the behest of the clan elders or the preceptor of a community.
Some of the prerequisites for niyoga were
The husband, whether living or dead, had no son
The niyogin (appointee) was a brother or a sapinda (a kinsman connected by the offering of the funeral rice ball to the manes of certain relation), or a sagotra (a kinsman from a common ancestor).
The sole purpose of co-habitation was to get the progeny to continue the lineage. The offspring of the union was considered to belong to the woman’s husband. There were injunctions to be followed to ensure that such unions did not degenerate into promiscuity. The association could continue only until a son was born. Afterwards, the relationship was deemed to be that between a father-in-law and a daughter-in-law. In case of violation of these injunctions, penance had to be undertaken.
There are incidents in the epics mentioning instance of niyoga. In the Mahabharata, Dhritarashtra, Pandu and Vidura were born in this manner through Sage Vyasa. Sometimes a king used this means to obtain a successor.
According to Vedas, a son is needed for performing propitiatory rites to one’s ancestors. He is also said to ensure their place in heaven. For this and other reasons, niyoga was practiced in very ancient times. However, this custom was discontinued more than 2000 years ago.