This document provides an introduction to polymers including their classification, structure, common types, and mechanisms of polymerization. Polymers are macromolecules composed of repeating structural units connected through polymerization reactions. They can be classified based on their structure as linear, branched, or cross-linked. Common addition polymers include polyethylene, polypropylene, polyvinyl chloride, and nylon. Condensation polymers include polyethylene terephthalate and polyamides. Polymerization occurs primarily through either addition or condensation reactions. Free radical addition polymerization follows initiation, propagation, and termination steps.