Sexual immorality refers to any type of sexual expression outside the boundaries of a biblically defined marriage relationship. The Bible defines sexual immorality as interpersonal activity involving sex organs that does not conform to Gods revealed laws governing sexuality. Sexual immorality is primarily used to refer to premarital sexual relations. The most common term in the New Testament for sexual immorality is porneia, which means "a surrendering of sexual purity". Sexual immorality is the "selling off" of sexual purity and involves any type of sexual expression outside the boundaries of a biblically defined marriage relationship.

The Bible strongly condemns sexual immorality. Sexual immorality is also connected to idolatry. The bodies of believers are the "temple of the Holy Spirit", and those who persist in unrepentant immorality and impurity cannot come into the presence of God. Sexual immorality can lead to psychological traumas for children and is said to be the main cause of the present dramatic increase in sexually-transmitted diseases.

To address sexual immorality, Christians must call it what it is - sin. Christians must hold fast to the teaching of Jesus Christ and turn away from their old selves.