Governance of Agile-Lean-DevOps projects

As senior and executive managers we know how to steer and govern projects in a waterfall style environment, but what happens when we change to a delivery system that might include agile, lean-agile and devOps?

Everyone is telling us we have to be more flexible, more adaptive and more comfortable with ambiguity, but at the same time no one is letting us off the hook about accountability.

How can we govern the delivery of valuable features for our organisation in such a construct?  What are we supposed to do? How are we supposed to act?