Polygamy means a system of marriage whereby one person has more than one spouse. Polygamy can be of two types. One is polygamy where a man marries more than one woman, and the other is polyandry, where a woman marries more than one man. In Islam, limited polygamy is permitted; whereas polyandry is completely prohibited.
The Qur’an is the only religious book, on the face of this earth, that contains the phrase ‘marry only one’. There is no other religious book that instructs men to have only one wife.
The context of this phrase is the following verse from Surah Nisa of the Glorious Qur’an:
"Marry women of your choice, two, or three, or four; but if ye fear that ye shall not be able to deal justly (with them), then only one."