APA
United Nations Environment Programme, . (1992). UNEP, two decades of achievement and challenge. Nairobi: United Nations Environment Programme.
Chicago
United Nations Environment Programme, . 1992. UNEP, two decades of achievement and challenge. Nairobi: United Nations Environment Programme.
Harvard
United Nations Environment Programme, . (1992). UNEP, two decades of achievement and challenge. Nairobi: United Nations Environment Programme.
MLA
United Nations Environment Programme, . UNEP, two decades of achievement and challenge. Nairobi: United Nations Environment Programme. 1992.