I was recently asked whether Catholics "believe in the rapture." And the answer is yes, except we only believe that Mary has been raptured.
First it must be admitted that at least two other humans have been assumed, body and soul into Heaven:
2 Kings 2:1-12
"And it came to pass, when the Lord would take up Elijah into heaven by a whirlwind...And fifty men of the sons of the prophets went, and stood to view afar off: and they two stood by Jordan....And it came to pass, as they still went on, and talked, that, behold, there appeared a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven....And Elisha saw it, and he cried, My father, my father, the chariot of Israel, and the horsemen thereof. And he saw him no more..."
"By faith Enoch was translated that he should not see death; and was not found, because God had translated him: for before his translation he had this testimony, that he pleased God."
It seems that Moses' body may been translated to Heaven after his death.
"But when the archangel Michael, contending with the devil, disputed about the body of Moses, he did not presume to pronounce a reviling judgment upon him, but said, 'The Lord rebuke you.'"
Thus any biblical Christian must admit that it is a matter of divine revelation that God assumed Enoch and Elijah.
Now Catholics believe that it is a matter of divine revelation that God also assumed Mary's body and soul into Heaven. Obviously, if Mary was without sin (see the Immaculate Conception) then it was fitting that she would not be held by the grave. Also, Christ was bound to "Honor your father and mother," and thus honored her by not allowing her to decay. Christ would not see Enoch and Elijah assumed into Heaven and then allow His very own mother to rot. The woman that bore Him, nursed Him, and stood by Him during His passion and death on the cross.
Catholics find the assumption of Mary prophesied in Psalm 132:7-8:
"We will go into his tabernacles: we will worship at his footstool. Arise, O LORD, into thy rest; thou, and the ark of thy strength."
Mary is the Ark of the New Covenant (see Revelation 11:19-12:1). The Lord ascended into Heaven and also brought His ark, just as King David took up residence in Jerusalem and escorted the ark to the same place.
Notice that Catholics don't speak of the "Ascension of Mary." Christ ascended by His own power. But Mary was passively assumed into Heaven by Christ. His power accomplished the honor. And thus in Revelation, Mary as seen as being "in Heaven."
You might also be interested in these Canterbury Tales posts:
What was the historical date of the Assumption of Mary?
The details on Holy Days of Obligations
Psalm 132 and the Assumption of Mary