The study of protease specificity provides information on active-site structure and function, protein-protein interaction, regulation of intracellular and extracellular pathways, and evolution of protease and substrate genes. Peptide libraries that include fluorogenic and binding tags are often generated by solid-phase synthesis. Even larger explorations of cleavage site preferences employ positional scanning libraries or phage display. Microarrays enable presentation of individual peptides to proteases, DNA sequences for capture of peptide nucleic acid encoded peptides, or nanodroplets containing soluble peptide sequences. These new methods continue to inform the design of chemical inhibitors and the identification of substrates of proteases.