One way I like to illustrate the change of mindset needed for an agile manager (or should I say leader), is to think of the organisation chart upside down.

The manager works for the team. Not the other way around. Their role is to provide the necessary support to enable the team to perform consistently at their best. They do this by making sure the team has everything they need to deliver, and by removing any obstacles that get in their way or slow the team down.

Of course there are also policy and governance aspects of a managers role within a corporation, which can't be ignored or necessarily described appropriately in this way. However I think it's still a useful way to think of a managers role in agile development.

A manager also has to balance their role supporting the team with the constraints of the organisation. And manage everyone's expectations accordingly. Often, this is not at all easy, or we'd all be fab managers! :-)

But when a manager has made this transition - made this change of mindset a habit - when it's the way they think - naturally - then they're well on their way to making the transition from manager to leader.

See also:
10 Key Principles of Agile Software Development
10 Good Reasons to do Agile Development
Top 10 Agile Development web sites