With increased environmental concerns and the rising demands for sustainable polymers, e.g., degradable polymers and chemically recyclable polymers, studies on ring-opening polymerization (ROP) of cyclic esters have been developed in recent decades. Biorenewable five-membered γ-butyrolactone (γBL) may be a desirable feedstock for the chemical synthesis of poly(γ-butyrolactone) (PγBL) or for the incorporation of γBL units into polyester chains to modify their properties. Although γBL is traditionally considered to be “nonpolymerizable”, some progress was recently made concerning the ROP of γBL. This mini-review is thus specifically focused on the ROP of γBL and its copolymerization with other cyclic esters.