The matter of polygamy in Islam is usually misunderstood by who wrongly grasp the aims of the Islamic legislation. This matter is completely regulated by Allah. The question of “ What is your opinion about the polygamy?” or “ Is it right or wrong?” is basically a forbidden question, bearing in mind that there is a deep difference between the polygamy as a general matter and a divine legislation and the polygamy as a personal option.   
In the first interpretation, discussing the polygamy is a matter of atheism since this discussion will be resistant to a divine legislation. In this meaning, Allah says,’ But no, by your Lord, they can have no Faith, until they make you (O Muhammad) judge in all disputes between them, and find in themselves no resistance against your decisions, and accept (them) with full submission’ (Surah An-Nisa’-65). But the second interpretation is possible as the polygamy is not suitable to everyone. Thus, there is a delicate and remarkable difference between the two interpretations.
Further, the polygamy has been, and still, known by many peoples. Islam did not create it from scratch; Islam regulates and restricts it. In other words, Islam does not impose the polygamy as a duty upon all Muslims; but it makes this matter permissible and puts the proper rules for regulating it.
Verily, Islam emerged when a man could marry to more than one woman. Many men adopted Islam while they had ten wives! Islam restricts the number of the women a Muslim man can marry. It restricts the number of the polygamy to only four wives without making it an obligatory duty. Clearly, Islam makes it permissible under two conditions- justice and capability.
If a man is not sexually satisfied by one woman, or if a wife is a barren woman, or if a Muslim man wishes to increase the total number of the Muslims through the reproduction, the polygamy will help him to achieve these acceptable targets. Here, the Islamic legislation (Shari’a) gives a Muslim man the permission to do so.
In this case, a Muslim man can marry to four women without violating the others’ honor or causing any social or religious sins like cheating or origin mixture which results in the self-reproach, or without getting rid of his existing wife, as the Christians do, to have the chance of getting married to another woman. 
Additionally, the polygamy is required especially in certain times. During wars, the number of women surpasses that of men. At the end of time, as our Prophets (may peace be upon him) informs us, the number of women will be bigger than that of the men. The Messenger (may peace be upon him) says, “ Among the conditions of the Resurrection Day are lifting of knowledge, spreading of ignorance, prevailing of adultery, drinking of spirits and departing of men and staying of women to the extent that fifty women are given just one guardian” (narrated by Al-Bukhary). In another hadith narrated by Ibn Muslim, the Messenger (may peace be upon him) says, “ A man will be seen followed by forty women for taking refuge in him because of the great number of women and the rarity of men”.  
 All in all, Allah does not put the legislation of the polygamy in vain; He does so for a certain interest and rationale, not as permission taken in time of necessity and neediness. In this concern, Allah says,
‘And if you fear that you shall not be able to deal justly with the orphan-girls then marry (other) women of your choice, two or three or four; but if you fear that you shall not be able to deal justly (with them), then only one or (the slaves) that your right hands possess. That is nearer to prevent you from doing injustice’. (Surah An-Nisa’- 4).