In practice, sustainable development is the use of natural resources in a manner that allows ecosystems to continue to function as natural ecosystems and biotic and abiotic interactions to maintain checks and balances are homeostatic. Historically, human activity has led to modification of nature that leads to (1) economic development, (2) biotic simplification (e.g., loss of biodiversity and simplified food chains), and (3) abiotic degradation (e.g., large changes in nutrient or light availability). Many experts believe that further biotic simplification and abiotic degradation are no longer sustainable, that the conflict between development and environment is the key to the quality of future human life on the planet, and that sustainability education should begin with young children. Thus, the central sustainable development focus is to balance quality of life with quality of the environment. The focus of the activity described in this article is to introduce and understand the concept of sustainable development by using ideas found in "The Lorax." While the activity as it is written is best suited for fifth grade, it has been used with minimal modification in grades 3-8. This activity is typically used as an introductory activity for a unit of instruction on sustainability and environmental problems, with appropriate follow-up activities tailored to meet specific school contexts. The activity is also suitable for use following lessons and activities on energy in both formal and informal (afterschool science clubs) settings. The recommended way of beginning this activity is small-group read-alouds using the Readers' Theater format. This type of integrated curricular reading is supported by both the anchor and grade-level standards of the "Common Core English Language Arts Standards" (CCSS-ELA). A project rubric and discussion sheet is available at www.nsta.org/SC1603.