And he will send his angels with a loud trumpet call, and they will gather his elect from the four winds, from one end of the heavens to the other. Matthew 24:31
This is a question that divides Christians. One group believes Christ will take His followers up with him and for seven years there will be tribulation on earth. This stems from interpretations of Daniel 7 and Matthew 24 that they believe indicate a rapture or “taking up” of believers. (Much like the book series Left Behind believed)
The other group believes when Christ returns He takes EVERYONE to be with Him and Judgment Day begins. Technically no one is left behind because the existence of everyone on earth ceases to be simultaneously. They point out that the word “rapture” never appears in the Bible. They feel this interpretation of a rapture and a 7 year tribulation has been forced on the scripture, but is not what it really means.
Personally, I believe in the second interpretation—that there will be one event, final and complete, as all people (believers and non-believers) gather to be with God. I cannot find a rapture in the Scriptures. It has to be imposed and forced into the word of God. I do find a final moment in the last day of earth when everyone is "called up" to face God on judgment day.