There isn’t any.

Certainly not enough to be able to draw a clear line between the two and start comparing the benefits of one against the other. Daniel Jones, the author of The Machine That Changed the World did a keynote at XPDay2008 and said from what he saw there wasn’t really much difference, apart from the name. In fact, when they were looking for a name for Lean they thought about using Agile.

Agile came from Lean, the related processes came from people studying Demming, The Toyota Production System or through convergent evolution. The two guys who invented Scrum are Japanese and that’s no coincidence.  When I started reading about Toyota and Demming it all simply made sense to me and explained where Agile came from.

Then I found an article written by Craig Larman on the history of iterative development and that wrapped it up: http://www2.umassd.edu/SWPI/xp/articles/r6047.pdf

There is no point spending any time discussing and trying to find differences between what is essentially the same thing just written in a different way.

It reminds me of how the Jews and Christians went their separate ways and then came the Muslims and then they split up into the Sunni and Shia’s. They’ve all been fighting bitterly for the last 2000 years but all worship the same god. Go figure!