APA

Thorsell J. W., Sawyer J., International Union for conservation of nature and natural resources, World Heritage Committee & World Congress on National Parks and Protected Area. (1992). World heritage twenty years later. Gland, Switzerland: IUCN, the World Conservation Union, in colla boration with UNESCO's World Heritage Committee.

Chicago

Thorsell J W, Sawyer Jacqueline, International Union for conservation of nature and natural resources, World Heritage Committee and World Congress on National Parks and Protected Area. 1992. World heritage twenty years later. Gland, Switzerland: IUCN, the World Conservation Union, in colla boration with UNESCO's World Heritage Committee.

Harvard

Thorsell J. W., Sawyer J., International Union for conservation of nature and natural resources, World Heritage Committee and World Congress on National Parks and Protected Area. (1992). World heritage twenty years later. Gland, Switzerland: IUCN, the World Conservation Union, in colla boration with UNESCO's World Heritage Committee.

MLA

Thorsell J W, Sawyer Jacqueline, International Union for conservation of nature and natural resources, World Heritage Committee and World Congress on National Parks and Protected Area. World heritage twenty years later. Gland, Switzerland: IUCN, the World Conservation Union, in colla boration with UNESCO's World Heritage Committee. 1992.