The　Caldecott　award　was　established　in　1938　as　the　first　award　for　children’s　picture　booksin　the　United　States．　Each　year　the　Caldecott　Medal　is　awarded　by　the　Association　for　LibraryServices　for　Children　（in　1938，　it　was　the　Section　for　Library　Work　with　Children），　the　children’sservice　division　of　the　American　Library　Association，　to　the　artist　of　the　most　distinguishedAmerican　picture　book　published　in　the　previous　year．　For　more　than　sixty　years　since　it　wasestablished，　it　has　had　a　great　influence　on　illustrators，　publishers，　librarians　and　those　who　areconcerned　with　children’s　books　not　only　in　the　United　States　but　also　all　over　the　world．　　　The　purpose　of　this　paper　is　to　examine　the　significance　and　the　cause　of　success　of　thisaward　by　studying　its　history　and　many　facts　behind　it．　lt　was　found　that　the　fact　“the　awardby　the　children’s　librarians　in　the　United　States”　has　supported　strongly　its　position　andauthority　for　many　years．　As　selecting　and　diffusing　good　children’s　books　have　been　recognized　as　the　children’s　librarians’　mission，　for　them　the　Caldecott　award　is　the　proof　of　theirprofessional　work．　Also　the　economic　and　social　situation　of　the　United　States　at　each　periodcannot　be　overlooked．　ln　the　United　States，　to　trace　the　award　means　to　trace　the　movementand　change　of　libraries　and　the　society．