You might not think it, but Cadillac knows a thing or two about building concept cars. General Motors' luxury line has managed to keep up with the times, building concepts that are both eco-friendly and stylish. These classy Cadillac concepts range from teeny-tiny city cars to behemoth luxury convertibles. If all you envision when you think Cadillac is an Escalade on 22-inch rims, then you need to head below and check out all of these killer concept Caddies.

The Converj is the most recent Cadillac concept car to receive the green light for production. The Converj, now known as the ELR, is an electric luxury coupe equipped with a range extender similar to the one found in the Chevy Volt. Cadillac says that the ELR will be powered by a T-shaped lithium ion battery, an electric drive unit, and a four-cylinder engine-generator. GM is expected to pull the wraps off of its newest electric car as early as the 2013 Detroit Auto Show.

"Glamour" is the unofficial name of this mysterious Cadillac concept. All anyone knows about the Glamour is that it's meant to be nostalgic in its design. There has been speculation that it may be a hardtop version of the Ciel concept shown off by Cadillac at the 2011 Pebble Beach Concours d'Elegance. The speculation is fueled by the fact that the two concepts share the same front-end, headlines and grille.

Everything about the World Thorium Fuel Concept is futuristic, from its flat-packed body to its nuclear-powered electric engine. Cadillac's future-forward concept car was designed by one Loren Kulesus. Kulesus envisions the WTC running on thorium, a mildly radioactive element that can't be weaponized. Scientists estimate that just 8 grams of thorium would be able to power a car some 300,000 miles.

Cadillac made a brief foray into the city car scene with its Urban Luxury Concept. The sharp supermini came fully equipped with scissor doors and enough sharp edges to fill a knife block. Caddy's mini concept gets its giddy up from a turbocharged 1.0-liter three-cylinder engine featuring electric assist.

"Beautiful" doesn't even begin to describe the Cadillac Ciel. The four-door convertible invokes memories of Cadillacs past with its long (125-inch wheelbase) and luxurious design. The Ciel is powered by a hybrid 3.6-liter V6 engine that puts out 425 horsepower and 430 pound-feet of torque. Ridiculous luxury additions include heated and cooled headrests, retractable blankets and aromatherapy controls installed into the armrests.