Since it was invented, the Ferris wheel has been a symbol of engineering innovation.

George Ferris unveiled his giant wheel in 1893 at the Chicago World’s Fair as a rival to the Eiffel Tower.   At that time, it was the largest single piece of forged steel ever made --and a mind-boggling 264 feet high.

Since then, versions of the wheel have become fixtures at theme parks and carnivals the world over.

But in 2000 a whole new era of giant Ferris wheels began with the London Eye–which offered visitors the chance to climb higher than ever before -- in fixed, climate controlled capsules. 

When Singapore opened its Singapore Flyer in 2008, it helped set in motion a global race to nab the title of world’s tallest wheel, with city officials trying to outdo each other with higher and more sophisticated structures.   

There are other giant Ferris wheel projects in the planning stages, including one in Japan and another in Changzhou, China with a unique spokeless design.   Yet, none of them threaten the plans of Dubai, which hopes to score the world’s tallest title in 2015.

Here’s a look at the current list of the world’s tallest Ferris wheels in motion –that is, until another city is upstaged.