I was asked this question via a FaceBook chat.  I anticipated after my answer they would sign-off with a quick “thanks” or try to justify why my answer did not apply.  I was pleasantly surprised when it turned out they were sincerely desiring to know what God had to say about the issue and were willing to follow His instructions.  Here is what I told them.

The Bible is very clear on that issue.  In fact, it is probably one of the most clearly answered questions in all of Scripture.  Typically “fornication” is the term used to refer to sex before marriage whereas “adultery” refers to sex after marriage with anyone other than your spouse.  The Greek word the King James Version translates “fornication” actually includes many forms of sexual immorality (incest, prostitution, harlotry, etc) and so is often simply translated “sexual immorality”, so as not to limit its meaning to fornication.  The Bible is clear that sex before marriage, and all sexual immorality, is a sin and warns of harsh penalties for those involved in it.

Here are just a few Scriptures – and there are many, many more – that address the issue:
(Acts 15:20; 1 Corinthians 5:1; 6:9, 13, 18; 10:8; 2 Corinthians 12:21; Galatians 5:19; Ephesians 5:3; Colossians 3:5; 1 Thessalonians 4:3; Jude 7; Revelation 21:8).

The Bible teaches self-control and complete abstinence before marriage and a one-man, one-woman relationship after marriage both physically and in the area of the thought life.