Polygyny : This is a form of marriage in which a man marries more than one woman. Polygyny as a polygamous form of marriage which is more popular than polyandry. 

Polygyny may be of the following types : 

• Sororal polygyny : In this type of polygyny, the man marries a number of women simultaneous who are sisters. 

• Non-sororal polygyny : In this type, the several wives of the man are not related as sisters of each other. 

Causes of polygyny may include the following : 

• When there are more number of females as compared to the males. 

• When women contribute economically to the family. 

• Sometimes the first wife may force the husband to bring in a second wife to reduce her work load at home. 

• Childlessness of the first wife can lead to the addition of a second wife into the family.

Polyandry : In this type of marriage one woman is married to several men at the same time.

Polyandry may be of the following types : 

• Fraternal : When several brothers are married to the same woman. 

• Non-fraternal : When the several husbands of the woman need not be related as brothers. However both of these types of polyandry should not be confused with ‘wife sharing’ or ‘wife-lending’.

Causes for polyandry may include the following : 

• Scarcity of women. 

• Heavy bride price. 

• Poverty and sterility of men