Avian antimicrobial peptides, classified as β-defensins, have been identified from bloods of chicken, turkey, and ostrich; epithelial cells of chicken and turkey; and king penguin stomach contents. β-Defensins are a family of antimicrobial peptides characterized by six cysteine residues forming β-defensin motifs that are also found in bovine, ovine, pig, and human. These peptides are active against a wide range of microorganisms including Gram-positive and Gram-negative bacteria, fungi, and yeast. Analysis of evolutionary relationships of vertebrate β-defensins showed that there might be a common ancestral gene between avian and other mammalian peptides. This ancient gene may have been passed down and evolved from species older than the oldest living birds, forming a β-defensin-like precursor molecule. This review describes potential applications of these peptides in health care products.