Benzylpenicillin, also known as penicillin G, is a narrow-spectrum antibiotic medication belonging to the class of drugs known as beta-lactam antibiotics. It is derived from the mold Penicillium and is one of the first antibiotics discovered and widely used in medical practice.

Benzylpenicillin works by inhibiting the synthesis of bacterial cell walls, leading to bacterial cell death. It is effective against a wide range of gram-positive bacteria, including Streptococcus species, Staphylococcus species, and some strains of Enterococcus.