Cancer remains the most prevalent and challenging disease to treat. It causes millions of deaths around the world every year, requiring advancement in treatment strategies. Nanoparticles (NPs), as drug delivery and targeting devices, are considered promising approaches for cancer treatment and early diagnosis. The current chapter focuses on polymeric NPs (PNPs) applied for the treatment and diagnosis of cancer owing to their amazing and unique properties as drug delivery vehicles. The colloidal systems of PNPs can be constructed from natural and synthetic polymers. The different methods for PNP production were discussed, including self-assembly, polymerization, nanoprecipitation, anti-solvent evaporation, emulsification solvent evaporation, emulsification solvent diffusion, freeze-drying, spray-drying, and salting-out. The analytical techniques for PNP physicochemical as well as toxicological characterization were highlighted. In addition, special attention was given to the classification of the natural and synthetic polymers used in the construction of the PNPs for cancer treatment. Furthermore, the possible natural resources of the biopolymer-fabricated anticancer PNPs were surveyed with a focus on the fish-derived polymers. This chapter summarizes up-to-date knowledge about the basis for developing tailor-made formulations effective for cancer therapy.