APA

International Union for Conservation of Nature and Natural Resources, International Union for Conservation of Nature and Natural Resources, United Nations Environment Programme & World Wide Fund for Nature. (1991). Caring for the earth. Gland, Switzerland: IUCN--the World Conservation Union.

Chicago

International Union for Conservation of Nature and Natural Resources, International Union for Conservation of Nature and Natural Resources, United Nations Environment Programme and World Wide Fund for Nature. 1991. Caring for the earth. Gland, Switzerland: IUCN--the World Conservation Union.

Harvard

International Union for Conservation of Nature and Natural Resources, International Union for Conservation of Nature and Natural Resources, United Nations Environment Programme and World Wide Fund for Nature. (1991). Caring for the earth. Gland, Switzerland: IUCN--the World Conservation Union.

MLA

International Union for Conservation of Nature and Natural Resources, International Union for Conservation of Nature and Natural Resources, United Nations Environment Programme and World Wide Fund for Nature. Caring for the earth. Gland, Switzerland: IUCN--the World Conservation Union. 1991.