This article will first examine the reasons that external plasticizer modification may not be necessary with polyurethane adhesives and sealants. It will then review the possible value that can be achieved from using added plasticizers. The article will also review the types of plasticizers that have been historically employed in polyurethanes as well as plasticizers that have been recently introduced to the market. Plasticizers are generally added to adhesive and sealant formulations to achieve a variety of properties such as lower viscosity, reduced hardness, and increased elongation. The selection of the plasticizer has to be made carefully to achieve these characteristics without loss of adhesion. The type of plasticizer that is utilized will depend on the properties that one is trying to achieve as well as its compatibility with the base polymer and other ingredients in the formulation. Plasticizers are often not necessary in polyurethane adhesives and sealants. The urethane polymer molecule is typically flexible enough at low temperatures that plasticization may not required.