In utero stem cell transplantation,which promises treatment for a host of genetic disorders early in gestationbefore disease effect stems from Ray Owen’s seminalobservation that self-tolerance,is acquired duringgestation.To date,in utero transplantation(IUT)hasproved useful in characterizing the hematopoietic stemcell.Recent observations support its use as an in vivomethod to further understanding of self-tolerance.Preclinical development continues for its application asa treatment for childhood hematolymphoid diseases.In addition,IUT may offer therapeutic options in thetreatment of diabetes among other diseases.ThusIUT serves as a technique or system important in botha basic and applied format.This review summarizesthese findings.