Power Up: Transforming Organizations Through Shared Leadership by David Bradford & Allan Cohen – Follows their Managing with Excellence book with a substantially researched body of work evaluating key post-heroic leadership characteristics – a key to leadership agility.
This book (and their previous) pre-dates Leadership Agility and has much of the underpinning to what makes Leadership Agility tick. Sharing responsibility is key agile enabler within an organization and the key to creating self-organizing teams.