English: Definitive hematopoietic stem cell pools emerge from intra- (AGM) and extra- (yolk sac and placenta) embryonic hematopoietic sites. When the circulation is established and functional, HSCs start their migratory journey and colonize the placenta, followed by the fetal liver that becomes the major hematopoietic organ until the bone marrow colonized by HSCs. The adhesion molecule VE-cadherin expression has been suggested to participate in HSC/progenitor migration but there is no functional data about the molecular mediators of HSC migration in the embryo. The colonization of the fetal liver and the bone marrow are dependent on β1 integrins and the CXCL12/CXCR4 chemokine/receptor axis.