The diverse functional repertoire of proteins promises to yield new materials with unprecedented capabilities, so long as versatile chemical methods are available to introduce synthetic components at specific sites on biomolecule surfaces. As a demonstration of this potential, we have used site-selective strategies to attach antifreeze proteins found in Arctic fish and insects to polymer chains. This multivalent arrangement increases the thermal hysteresis activity of the proteins and leads to materials that can be cast into thin films. The polymer-protein conjugates retain the ability of the proteins to slow ice growth in subzero water and can inhibit ice formation after attachment to glass surfaces. These inexpensive materials may prove useful as coatings for device components that must function at low temperature without ice buildup. The polymer attachment also allows higher thermal hysteresis values to be achieved while using less protein, thus lowering the cost of these additives for biomedical applications.