This paper describes the molecular recognition of amino acids by cucurbit[8]uril (Q8) and by the 1:1 complex between Q8 and methyl viologen (MV) in purely aqueous solution. These hosts are known to bind aromatic peptides with high affinity and sequence specificity, but prior work has focused on only a small subset of amino acids. In an effort to elucidate the scope and limitations of amino acid recognition by Q8 and Q8•MV, a comprehensive examination of the 20 genetically encoded amino acids was carried out by 1H NMR spectroscopy and isothermal titration calorimetry. We find that both Q8 and Q8•MV bind measurably to only tryptophan, phenylalanine, and tyrosine. These results demonstrate that Q8 and Q8•MV are highly selective in the context of all genetically encoded amino acids and are therefore promising for the development of recognition-intensive applications involving peptides, proteins, and proteomes.