Aldo Leopold's "A Sand County Almanac" is one of environmental philosophy's seminal texts, and Callicott is widely considered to be the leading contemporary exponent of Leopold's land ethic. Callicott's book "In Defense of the Land Ethic" (1989) explores the intellectual foundations of Leopold's outlook and seeks to provide it with a more complete philosophical treatment; and a following publication titled "Beyond the Land Ethic" (1999) further extends Leopold's environmental philosophy. Callicott's "Earth’s Insights" (1994) is also considered an important contribution to the budding field of comparative environmental philosophy; a special edition of the journal "Worldviews: Environment, Culture, Religion" (Vol. 1, Number 2) was devoted to scholarly reviews of the work. Callicott is co-Editor-in-Chief with Robert Frodeman of the award-winning, two-volume A-Z "Encyclopedia of Environmental Ethics and Philosophy", published by Macmillan in 2009. He is also author of numerous journal articles and book chapters in environmental philosophy and has served as editor or co-editor of many books, textbooks, and reference works in the same field.