This chapter contains sections titled: A Brief History of Ziegler-Natta Catalysts Definitions and Nomenclature Characteristics of Ziegler-Natta Catalysts Early Commercial Ziegler-Natta Catalysts Supported Ziegler-Natta Catalysts Prepolymerized Ziegler-Natta Catalysts Mechanism of Ziegler-Natta Polymerization