Penicillins are a class of antibiotics that work by inhibiting bacterial cell wall formation. Alexander Fleming discovered penicillin in 1928 and its widespread introduction marked the beginning of modern antibiotic chemotherapy. Further research led to developments like semi-synthetic penicillins with broader spectra. Penicillins are commonly used to treat bacterial infections like strep throat and penicillin-sensitive staph infections as well as syphilis. They can be administered orally or parenterally and have benefits but also side effects like allergic reactions. Resistance develops through enzymes and structural changes, presenting challenges to penicillin's future role in infection treatment.