We present a proof of principle for the phenomenon of the tragedy of the commons, a concept upon which many theories on the evolution of cooperation are built. We establish the tragedy in the context of a general chemostat model with two species, the cooperator and the cheater. Both species have the same growth rate function and yield constant, but the cooperator allocates a portion of the nutrient uptake towards the production of a public good -the ?Commons? in the Tragedy- which is required for growth. The cheater does not produce the public good, and can allocates all nutrient uptake towards its own reproduction. We prove that when the cheater is present initially, both the cooperator and the cheater will eventually go extinct, hereby confirming the occurrence of the tragedy. We also show that without the cheater, the cooperator can survive indefinitely. Finally, we investigate modifications to the cooperator's growth characteristics which enable it to drive the cheater to extinction. Whether such modifications can arise as a result of evolutionary processes is an interesting question. This is joint work with Hal Smith (Arizona State) and Eric Foxall (Alberta), and David Finch and Martin Schuster (both at Oregon State).