Hertzian　indentation　was　used　to　evaluate　the　local　strength　of　glasses　and　to　estimate　residual　stresses　in　strengthened　glasses.　It　was　found　that　initiation　of　Hertzian　crack　in　glasses　depends　on　the　mean　stress　within　a　surface　thickness　related　to　material　properties,　but　independent　of　the　peak　stress.　The　maximum　mean　stress　for　crack　initiation　was　a　constant　and　was　defined　as　the　local　strength　of　the　specimen　at　the　contact　position.　Indentation　experiments,　using　alumina　spheres　with　various　sizes　as　indenters,　were　performed　on　unstrengthened　and　strengthened　glasses,　respectively.　The　results　showed　a　good　stability　in　the　local　strength　and　a　good　agreement　between　the　residual　stresses　measured　by　the　present　method　and　by　a　polarizing　device.　In　addition,　the　potential　merits　of　this　method　are:　a)　Nondestructive　and　in-situ　measurement　of　strength　can　be　performed　without　using　a　standard　specimen　and　a　rupture　test;　b)　Strength　proof　test　and　strength　comparison　can　be　easily　preformed.　(C)　2002　Published　by　Elsevier　Science　Ltd.　All　rights　reserved.