The interaction of polymers with their environment depends largely on the functional groups they carry. Interfaces between different polymers or between polymers and other surfaces can be strengthened through the design of molecular interactions such as hydrogen bonding and through the control of polymer architecture. The placement of functional groups at polymer chain ends or in well-defined segments can determine the ultimate properties. Three-dimensional synthetic polymers such as dendrimers can be fashioned to encapsulate reactive sites or provide highly controlled surfaces and interfaces.