Penicillin is an antibiotic used to treat certain types of bacterial infections, such as pneumonia, meningitis, or strep throat. There are different types of penicillin with different mechanisms of action. All forms are derived, at least in part, from a fungus known as Penicillium chrysogenum.

The issue of a patent for penicillin was a controversial problem from the beginning. Chain believed that obtaining a patent was essential. Florey and others viewed patents as unethical for such a life-saving drug. Indeed, penicillin challenged the basic notion of a patent, considering it was a natural product produced by another living.