The teacher of an environmental science elective describes the “Who's in the Zoo?” project that she designed to help students achieve conceptual depth in understanding biomes. The project uses the framework of the 5E learning cycle—engage, explore, explain, elaborate, and evaluate—and takes six one-hour class periods to complete. The writer describes the progress of the project for all six class periods and notes that the activity works by linking biomes to a place that most students have visited, thus maintaining student interest in the process. A sidebar presents a set of detailed student instructions for the project.