This document classifies and describes various parasites. It divides parasites into protozoans and metazoans. Protozoans are further divided into ciliates, sarcomastigophorans, and apicomplexans. Various parasites are listed under each category, along with the diseases they cause. Metazoans are divided into nematodes, platyhelminths, and trematodes. Different parasitic nematodes, cestodes, and trematodes are described along with their transmission methods.