Positiveshynessisauniversalemotionwiththespecificsocialfunctionofregu-latingourinteractionsbyimprovingtrustandliking,andshowingpoliteness.Thepresentstudyexaminedearlyinfantproductionofcoysmilesduringsocialinteractionsasameasureofpositiveshybehavior.Eighty4-month-oldswereexperimentallyobservedduringthreetypesofinteractionsinfrontofamirrorinwhich(1)theinfantonlyseeshimorherself,(2)theinfantonlyseestheotherperson(mother,father,orstranger),and(3)theinfantseesbothhimorherselfandtheotherperson.Infantsproducedmorecoysmilesduringtheinteractionwithastrangerthanduringtheinteractionswiththeirmotherortheirfather,orwhentheycouldseeonlythemselvesinfrontofamirror.Infantsalsoproducedmorecoysmileswhentheycouldseetheirself-reflectionduringtheinteractionthanwhentheycouldnot.Ourresultssupporttheassumptionthatcoysmilesindicateanearlyemergingemotionalreactionwithanimportantadaptivefunctionduringsocialsituationsinvolvingnovelper-sonsandwhenspecialattentionisgiventothechild.Bytheageof1–2months,infantsstarttosmileduringsocialengagementsandinteractionswithadults(Messinger&Fogel,2007).Infants'socialsmilesarenormallyproducedasareactiontoparentalfacialexpressionsandattention(Lavelli&Fogel,2005)andareoftencombinedwithgazetothefaceoftheparentandpositivevocalizations(Weinberg&Tronick,1994;CorrespondenceshouldbesenttoCristinaColonnesi,ResearchInstituteofChildDevelop-mentandEducation,UniversityofAmsterdam,NieuwePrinsengracht130,1018VZAmster-dam,theNetherlands.