I'm going to choose to narrow this down to Western Europe specifically, because as of right now it is a vrey broad question. Furthermore I'm looking at the later Early Modern Period, from the mid-1300's to the mid-1500's. I'm also drawing from this blog post I made on the topic.
In the Early Modern period, marriage could be undertaken in a vast array of different ways. According to Stone and Dabiwhola, up to the eleventh century (1000) causal polygamy and bigamy was common and divorce and concubinage were both easy come and easy go among the laity and the non-royal and non-upper classes. Marriage, in the early middle ages was seen and treated much like
"a private contract between two families concerning property exchange, which also provided financial protection to the bride in case of the death of her husband or desertion or divorce by him. For those without property, it was a private contract between two individuals, enforced by the community sense of what was right. A church ceremony was an expensive and unnecessary luxuty, especially since divorce by mutual consent followed by marriage was still widely practiced." [4]
Indeed, it was not until the 1215 Fourth Lateran Council that the church prohibited incest, asserted that only a indissoluble monogamous marriage was appropriate, and declared that there must be a publication of banns before a marriage could take place. The banns were a loud public announcement on behalf of the marrying couple for three weeks prior to the marriage, to allow people to dispute or contradict it. Evidence shows that this was followed irregularly among the lower classes, to say in the least.
Over the course of the next couple of centuries (1200-1400) the definition of what an appropriate marriage was developed rather slowly. Eventually it came to take a five-step process:
A contract between the the families for financial arrangements and exchanges of property (in cases where there were finances or property to be exchanged.)
The spousals--the exchange of promises spoken between the husband and wife in front of witnesses.
The proclamation of banns for three weeks prior to the marriage.
The wedding in and the blessing of the Church (when the wedding actually took place in a church)
Sexual Consummation. (Legally, anyhow, surviving evidence shows sexual consummation would usually happen among the lower classes before the marriage)
However, this was just the process in theory. "In remote [or rural areas]...the bethtothal ceremony itself, the 'handfast' continued to be treated by many of the poor as sufficient for a binding union without the blessing of the Church. There is some evidence that...quite large numbers of the poor were not getting married in church in the late seventeenth century (late 1600s)." [4]
With the Reformation, all of this would change. Sex and marriage was essential to the Reformation’s worldview. It also became essential to the Counter-Reformation. Envoys at the Council of Trent pointed out that some of Luther’s critiques were correct: “citing information garnered from an extensive visition of Bavaria in 1558, [an envoy] painted a dark picture. The vast majority of the parish clergy was ignorant and infected with heresy. Out of a hundred only three or four were not secretly married or keeping concubines, to the great scandal of the faithful.” Furthermore, it was common for upper-class men to clandestinely marry or promise marriage to women of lower station to ‘get into their pants,’ and then, if she got pregnant, to deny ever having been married. [1, 2]
The result was the Tamesti, which stated that “whereas clandestine marriages had previously declared valid, though blameworthy, all would be deemed invalid unless celebrated before a priest and at least two witnesses.” In O’Malley’s view “No single provision of the entire council affected the Catholic laity more directly than Tamesti… The approval and implementation of Tamesti meant that in the future the church recognized no marriages between Catholics as valid unless it had been witnessed by a priest.” The intention and effects of Tamesti were, in a way, feminist in the sense that they sought to protect and enfranchise women against being abandoned due to clandestine marriages. [1,2,3]
This debate, probably more than anything else, has had a profound impact and influence on our lives today. For example, in modern times we often consider anything that has to do with sex or sexuality as ‘private’ and something that should occur ‘behind closed doors.’ In the sixteenth, seventeenth, and even the early eighteenth centuries this was not necessarily the case (though it became increasingly so as time progressed). In fact it was not abnormal for a wedding party to watch the couple on their first night, nor was it uncommon for sexual acts to take place in a bar or in public, and witnesses would think very little of it. [1,2]
Again, this was a period where entire families would share the same bed and children were likely to know just how their parents made new siblings. The splitting of the private and public world that happened as a result of the Reformation and Counter-Reformation had an impact on the architecture of the home and the attitudes around sex. Occurring first among the upper classes, who were likely already accustomed to formalized and public marriages. They then began to be adopted by middle and lower classes, slowly at first and then with increasing rapidity, as shown by the architecture of the home: “Bedchambers—and the beds themselves—slowly shifted from being common living areas (in lower-class homes) or sites for social gatherings (in upper-class ones) to being what they are today—private space for the single person or couple who sleep in them.” [1, 2, 3.]
[1] Trent, What Happened At the Council. Rev. Dr. John W. O’Malley
[2] The Canons and Decrees of the Council of Trent, trans. Rev. H.J. Schroeder
[3] Locks and Lavatories: The Architecture of Privacy Philippe Planel
[4] The Family, Sex, and Marriage in England, 1500-1800, Lawrence Stone
[5] The Origins of Sex, Faramerz Dabhwhola
Further discussion of this in these blog posts: Sex Behind Closed Doors: Marriage, and the Invention of Privacy, Martin Luther: Sex, Scat, and the Protestant Revolution