Islam permits a man to marry up to four wives, but only under strict conditions of justice, and the Quran warns that if one fears being unjust, then one should marry only one. In practice, the great majority of Muslim marriages today are monogamous.
The fuller answer
The verse was revealed after the battle of Uhud, when many men had died and many widows and orphans needed protection. Polygamy existed everywhere in the world at the time and had no limit; Islam limited it to four and attached conditions: equal treatment in support, housing and time, and the consent of the law. The Quran itself says that one cannot be fully equal between wives, however much one tries.
A woman can make a condition in her marriage contract that her husband will not take another wife, and this is accepted by most schools. Some Muslim-majority countries, such as Tunisia and Türkiye, have banned polygamy, and others require a court's or wife's approval. Muslims differ on how widely it should be practised today.
And if you fear that you will not deal justly with the orphan girls, then marry those that please you of [other] women, two or three or four. But if you fear that you will not be just, then [marry only] one or those your right hand possesses. That is more suitable that you may not incline [to injustice].
And you will never be able to be equal [in feeling] between wives, even if you should strive [to do so]. So do not incline completely [toward one] and leave another hanging. And if you amend [your affairs] and fear Allah - then indeed, Allah is ever Forgiving and Merciful.
This answer follows the mainstream Sunni understanding and is general learning, not a fatwa. Where Muslims differ, the answer says so. Have a question of your own? Write to us.
