Peptides are chains of amino acid residues connected via amide linkages. Peptides composed up to 10 amino acid residues are referred to small peptides, while those with up to 100 residues are known as (poly)peptides. A peptide moiety forms prime constituent of not only proteins but also aspartame, an artificial non-saccharide sweetener. Peptides serve various functions in organisms, especially the peptide hormones which play important roles in signal transductions. Some synthetic peptides can also be used as reagents for biochemical research and in pharmacy.