A Camelid VHH Antibody (also called single-domain antibody, sdAb or Nanobody by Ablynx) is a peptide chain of about 110 amino acids long, comprising one variable domain of a heavy-chain antibody. Like a whole antibody, it is able to bind selectively to a specific antigen. Single-domain antibodies allow a broad range of applications in biotechnical as well as therapeutic use due to their small size, simple production and high affinity.