Polygamy, as used in this Bible study, is defined as one man being married to more than one woman, or one woman married to more than one man.
Strictly speaking, the Old Testament practice of one man having multiple wives at one time is known as polygyny. An important fact to remember regarding polygamy is that it has fundamentally always been something that only rich men could take advantage of.
Perhaps the most well known case of modern polygamy is with the U.S. based religious group called the Mormons. The group's founder, Joseph Smith, as well as early leaders such as Brigham Young, were married to more than one woman at a time. In 1852 some of the church's leaders began to openly admit that plural marriages had taken place in secret. At its peak, the practice of polygamy affected between 20 to 30 percent of Mormon families.
The Bible is a bit confusing regarding polygamy. Genesis seems to say that, right from the start, God intended marriage to be between only one man and one woman (Genesis 2:23 - 24). We find later, however, that several individuals, many of whom had great faith, had more than one wife at a time.
The Old Testament is clear about its view regarding polygamy. Although God himself ruled Israel when they came out of Egypt, he knew there would likely be a time when they would want a human king over them.
Although the Lord warned any future Israelite king that they should not possess many wives, He did not outright ban them from practicing polygamy or state they could only have one wife at a time (see Deuteronomy 17:14, 17). Additionally, what few realize, is that no passage exists that forbids multiple wives among Israel's tribes.
God knew the rulers over his people would pursue multiple wives like all the other nations. He warned them not to have many women, especially from outside the twelve tribes of Israel (pagans), so that they could not be lead astray. Unfortunately, men like King Solomon did not follow this advice. Although he was wise, he nevertheless married many foreign women who turned his heart away from the Eternal (see 1Kings 11).
By the time of the early church, the general practice of polygamy had largely died out in the Roman Empire. Although the Romans themselves did not practice it, they did divorce and remarry when they wanted to change spouses. A few exceptions existed such as Herod the Great, who was a polygamist.
Although the New Testament does not directly address this polygamy, the fact that it says almost nothing points to its decline.
There are several Scriptural-related passages on marriage, in the writings of Paul, which strongly infer that polygamy was not an acceptable New Testament practice.
For example, he wrote to Timothy that one of the traits to look for in a good church leader was that he was "the husband of one wife" (1Timothy 3:2, 12). He also wrote this admonition to Titus as well (Titus 1:5 - 6). The church in Corinth was told one way to help avoid sexual immorality was to ensure that each person had one mate (1Corinthians 7:2).
What should Christians do in regard to polygamy? They should submit to the laws in the land they live in so long as they do not conflict with what the Bible teaches (see Romans 13).
A large percentage of countries in the 21st century have laws against such marital arrangements (with the exception of countries governed or influenced by Islam). Modern-day believers should reject this ancient practice of polygamy and stick to one woman for one man.