The moustached tamarin (Saguinus mystax) is a small marmoset that lives in the upper Amazon regions of Brazil and Peru. It is characterized by white moustache-like facial hair and is arboreal and diurnal, feeding on fruit, flowers, insects, and tree sap. It lives in multi-male, multi-female groups of about seven individuals; typically only the oldest female breeds while other group members act as helpers, assisting with infant care and carrying. Distinctive social structures and behaviors are known, including the birth of twins and occasional infanticide by mothers observed within groups. Its conservation status is Near Threatened.