This research paper discusses the different definitions of ecocriticism highlighting their similarities and differences to reach out a definition that is most accurate and comprehensive. The paper also studies the nature of ecocriticism, its history, importance and concerns. Then a brief history of American ecocriticism is surveyed. After that, the paper analyzes in detail Aldo Leopold's masterpiece A Sand County Almanac as an example of a non-fiction work that calls for respecting nature in general. This paper attempts to both show how far Leopold has redefined the relation between man and nature, and also tries to study the famous and significant land ethic theory. Moreover, the values of wilderness suggested by Leopold have been examined to reflect the importance for readers to protect, love and respect nature