Polyandry is a form of polygamy where a woman has more than one husband at one time. In the United Kingdom, this is illegal.
Institutionalised polyandry is rarer than polygyny. The most famous example of polyandry, in Hindu culture, for example, occurs in the Mahabharata where the Pandavas are married to one common wife, Draupadi. Today it is almost exclusively observed in the Toda tribe of India, where it is sometimes the custom for several brothers to have one wife. In this context, the practice is intended to keep land - a precious resource in a populous country like India - within the family.
See Polyamory for the main article on this area.