In the first part, an overview of polyketides and polyketide biosynthesis is presented. A rationale for investigating polyketide biosynthesis is also presented. In the second part, the contributions of genetics and molecular biology on investigations into erythromycin biosynthesis are summarized. The impact of these fields on biosynthetic engineering is also explained. In the final part, the enzymology of the erythromycin polyketide synthase is discussed.