Mammoth Cave National Park was established in 1941 to protect the unparalleled underground labyrinth of caves, the rolling hilly country above, and the Green River valley. Since then, ongoing study and exploration have shown the park to be far more complex than ever imagined, hosting a broad diversity of species living in specialized and interconnected ecosystems. The park's challenge is to balance these remarkable and sometimes fragile living networks with the public's enjoyment of them. The key to that balance is knowledge, and the park's new environmental monitoring programs will provide that understanding.