Recently biochemists have been able to construct organisms that can produce unnatural amino acid containing proteins with high efficiency and fidelity. Improved expression methods for unnatural protein production have allowed assessment and tuning of unnatural synthetases permissivity. Permissive unnatural amino acid synthetases should significantly expand the tool set available for manipulation of proteins. Specific applications on probing protein-protein interactions, studying protein folding, exploring posttranslational modifications, and engineering biomolecular interactions will be will be discussed.