Polymer molecules are monomers contiguously connected by covalent bonds in a chain-like fashion. The monomers themselves are groups of atoms, and can be either identical repeat units (as in polyethylene or polyuridylic acid) or chemically different units (as in a protein molecule or a deoxyribonucleic acid (DNA) containing different bases). Depending on the chemical nature of the repeat units of the polymer, the number of monomers per chain, and the nature of the solvent in which the polymer is dispersed, the molecule can assume different sizes and shapes such as globular, coil-like, and rod-like. It might seem at the outset that it is necessary to treat each polymer in a given solvent condition as a unique case by accounting for the specic chemical nature of the polymer and solvent. However, it turns out that there are certain universal laws that can describe average polymer conformations. It is possible to surrogate the local degrees of freedom of chemical specicity into a few parameters and obtain useful coarse-grained models in order to understand the universal properties of polymer chains.