Παραπομπή σε μορφή APA (7η εκδ.)

Orr, D. W. (2011). Hope is an Imperative: The Essential David Orr. Island Press/Center for Resource Economics : Imprint: Island Press.

Παραπομπή σε μορφή Chicago (17η εκδ.)

Orr, David W. Hope Is an Imperative: The Essential David Orr. Washington, DC: Island Press/Center for Resource Economics : Imprint: Island Press, 2011.

Παραπομπή σε μορφή MLA (8th εκδ.)

Orr, David W. Hope Is an Imperative: The Essential David Orr. Island Press/Center for Resource Economics : Imprint: Island Press, 2011.