From the Bible
Although God fellowshipped with Adam and Eve daily, He never told them they were naked (Genesis 2:25, 3:11). Additionally, we don't know how long this took place.
God declared His handiwork, the naked human, good (Genesis 1:31, Acts 10:15, Isaiah 5:20).
Although nudity was God's choice, clothing was man's choice. More importantly, Adam and Eve clothed themselves out of fear, and as a result of sin (Genesis 3:7, 3:11).
Some prophets were known to prophesy nude and were thus recognized as prophets because of their nudity. Saul, and all those who went before him, prophesied naked "all day long" after the Holy Spirit of God came on them and the people recognized them as prophets partly because of their state of dress (1 Samuel 19:23-24). Additionally, the Lord once commanded Isaiah to go naked in front of everyone for three years as a sign (Isaiah 20:2-4). Also see Micah 1:8.
David danced openly before all of Israel, as an "act of worship" of God, wearing only a "linen ephod" -- a long vest like garment (2 Samuel 6:14). Micah, his wife, claimed he acted as a "vulgar man would," and God cursed her for such accusation (2 Samuel 6:16, 20-23).
One follower of Jesus fled naked (Mark 14:51).
When they crucified Jesus, he was completely naked (Matthew 27:35, Luke 23:34, John 19:23), yet "He was without sin" (Hebrews 4:15).
Peter, one of the twelve disciples of Jesus and the first leader of the Christian Church, fished naked. He was fishing naked when Jesus came to him after His resurrection and Jesus said nothing about it (John 21:7).
Neither clothes nor nudity will keep you or others from sinning (Acts 5:42, Colossians 2:8, 2:23, 2 Peter 2:19-20), but only Jesus Christ and His Holy Spirit can (Galatians 5:16).
In General
Both Jewish and Christian baptisms originally required people to be completely naked -- even mass baptisms with men, women, and children together. It symbolized the work Christ accomplished for the newly "saved" believer.
Indoor plumbing is a rather new invention, and so public bathing was once a common practice. Individuals, and whole families, including Christians, bathed together at the public bath.
The word gymnasium originally meant "a place where you train in the nude." At one time, it was standard practice for athletes to train and compete in the nude.
Volleyball first became popular at a nudist resort in France. It was originally called mintonette, and was renamed after one spectator commented how the game involved "much volleying."
All scriptures NIV unless otherwise noted.