What is the most established used car buyers guide?

The Kelley Blue Book in its modern form was first published in 1926. However, Les Kelley, owner of the Kelley Kar Company, had been publishing a less extensive list of used car values since 1918.

When Kelley's judgment of car values came to be trusted as accurate and reliable by automobile dealers and enthusiasts, others began to request his lists of values for their own use. The Kelley Blue Book as it is recognized today originated from these lists and has been used ever since. Edmunds, another prominent car pricing guide, was first published in 1966. Their website was established in 1994, and in 2006, it replaced the physical pricing guidebooks.