Sometimes, concepts test particular ideas - for example, they could be a testbed for exterior and interior colors and materials, new controls and dashboard layouts, variations on packaging (where to put things), and the like. Those ideas can be rather subtle.

Other concepts are designed to help designers think out of the box. One example of that is the Jeep Treo - it's not meant to actually be produced, but was a study to consider what cars be like when fuel cells were common, 10-20 years down the line, and how that would affect styling. Without a large engine in front, for example, the Treo allows drivers to actually look through the grille. The Treo feels surprisingly spacious though the interior's quite small, because there's no traditional dashboard ledge underneath the windshield; the front is largely empty.