That's a hard question. You may as well ask the same question of Babylon, the holy grail or Noah's ark. All of these things were written about by ancient philosophers, but does that make them real? As a scientist, I sort of lean towards the idea that until someone discovers the sunken remains of an entire civilization, I will treat Atlantis as a myth. But this is really a personal decision. The only known reference we have of Atlantis from the ancient philosophers is in the writing of Plato. But we know for a fact that a lot of writings from this time period were lost.

To me, there are three possibilities:
1. Plato invented the idea of Atlantis to illustrate a point he was trying to make in his writings.
2. Plato made up the story of Atlantis, but it is based on a true story: perhaps a flood which ended the famous Minoan civilization in ancient Greece.
3. Atlantis was real, and modern anthropologists just haven't found its remains yet.

All three possibilities are equally valid, in my mind. The ocean is a HUGE area, and the deep ocean is very hard to study, so it's impossible to say that Atlantis doesn't exist just because we haven't found it.

Basically, we'd have to map the entire ocean floor at a very high resolution, which we are trying to do but this is expensive and takes time. Look at how long it took us to find and photograph the Titanic, and we are still looking for Amelia Earhart's plane.

Sunken boats and planes are much smaller objects than a lost civilization, but it's very likely that Atlantis, if it did exist, is now buried under a thick layer of mud, and Plato didn't leave us very good clues as to where it might be. On the other hand, Plato often used real objects to represent abstract concepts in his writings, and so the idea that he invented the story of Atlantis is also quite likely.

It is amazing to me that we are still fascinated by Atlantis thousands of years after Plato wrote about it. I think this is because humans like to believe in mysteries (the Bermuda triangle, for example), and we also like to believe in ancient civilizations that were somehow better than our own (more beautiful, or more spiritual, or more powerful). As far as science, we'll just have to wait until technology makes the ocean easier to study AND until there is enough interest and money for deep-ocean exploration projects. (Why Mars gets more attention than the deep ocean is beyond me!)

One web site with more information on Atlantis is: Atlantis

Seems it was a bit of both, actually- this sort of thing tends to happen during games of "telephone" lasting thousands of years.

There is much debate but it seems the most promising candidate for Atlantis is the island of Thera, also called Santorini, in the western Mediterranean. Thera is not in the Atlantic Ocean, where the tale says Atlantis should have been. The standard version of the story comes from Plato, who lived long after the demise of Atlantis. Plato heard the story from the Egyptians, who might have had contact with the Atlantians.

Anyway, the discrepancy could come from Plato's statement that Atlantis was "beyond the Pillars of Hercules", an ancient name for Gibraltar, which would have put Atlantis in the Atlantic Ocean. It turns out that near Plato's home in Greece, there are some lesser-known rocks called the Pillars of Hercules. The large size of Atlantis could be a due to a mistranslation. "Bigger than Libya and Turkey (then called Asia) together" might have been originally written as "between Libya and Turkey"- which would be a good description for the location of Thera.

Thera used to be a large volcano, but it had a huge eruption thousands of years ago, and there's not much left of it. The island is much smaller, and it doesn't have the tall volcano anymore.

Before the eruption there were no instruments for sea navigation, so people who wanted to sail there would have just headed in the general direction and waited until they saw the volcano. Without the volcano Thera would have been very hard to find, because it would hide behind the curvature of the Earth. With no landmarks in the open sea, it would have been easy to miss the island completely, hence the "sinking" part of the story. The island probably did sink a bit, too, because the magma chamber underneath it would have been suddenly depleted. There also would have been a "splash" sloshing the Egyptians with a tsunami, a huge plume of ash, and the sudden disappearance of Atlantian ships. You can see how the whole story might have started. Ancient ruins have been found on Thera and in shallow waters nearby. The civilization was advanced for its time- they certainly didn't have any modern technology, but they did have things like sinks with hot and cold running water, which would have astonished the Egyptians or any other visitors. Some of the things found in the ruins match details from Plato's story.

This whole scenario is at least credible, unlike many other Atlantis variants involving axis shifts, the Bermuda Triangle, doomsday technology, etc. Those stories are 100% myth.

This all reminds me of an even more ancient myth which might have some truth in it: Noah's flood. At the end of the last ice age the sea level was hundreds of feet lower, but as the glaciers melted, the sea rose. The Mediterranean Sea, the Black Sea, and the Persian Gulf are now just barely connected to the main ocean, but when the sea was lower, these pinch points were dry land. There was still water in the enclosed basins, but these inland seas were below the level of the main ocean (like the Dead Sea and the Salton Sea, but much larger). As the ocean filled with meltwater, it burst through the pinch points and caused three huge floods. The Mediterranean Sea and Black Sea even hold some submerged ancient villages that were high and dry before the floods.