β-Thromboglobulin (β-TG), or beta-thromboglobulin, is a chemokine protein secreted by platelets. It is a type of chemokine (C-X-C motif) ligand 7. Along with platelet factor 4 (PF4), β-TG is one of the best-characterized platelet-specific proteins. β-TG and PF4 are stored in platelet alpha granules and are released during platelet activation. As a result, they are useful markers of platelet activation. β-TG also has multiple biological activities, for instance being involved in maturation of megakaryocytes.