Is management support needed to use an Agile methodology?

Question: What kind of support do you need from management (or your client) in order to start using an Agile Process?

Okay, here's a contrarian answer:

I DON'T BELIEVE THERE IS ANY BUY-IN OR SUPPORT NEEDED IN ORDER TO APPLY AGILE!

Agile is a competitive advantage in and of itself. (If it wasn't, why bother? Surely not only because "Agile good, waterfall bad".)

The business environment itself demands agile because it is changing rapidly, and agile is the winning response wherever the cost of doing/redoing/re-re-doing (agile) is less expensive than perfecting the design before doing anything (waterfall).

The pyramids weren't built using agile methodology because they couldn't pile up a bunch of 10-ton stone blocks and then move them around until they got it right.

But almost all knowledge-based projects (such as software) are different using today's tools.

So let's say a client wants me to create a fat binder of exacting specs before writing software (ie traditional waterfall). I can't make the project agile, but I (and whatever team or part of it I'm with) can iterate those specs instead of taking notes for 6 months and then dropping off the fat binder. I can also do metrics on how the requirements even for already communicated specs are changing, and thus show how that fat binder is always going to be x% of date with y effort devoted to updating them, where that x% drops off as the y effort is increased, but with diminishing returns.

Sure, it would be even better if I can convince the project drivers that building a prototype that users can verify would be even better than than the book alone, but if I can't convince them, I can still deliver whatever result I'm committed to, with the resources I control, in a greatly advantageous and competitive way.

My point is: you can always run your little corner of the world very successfully in an agile fashion.