This article explores the changing expectations and contested identity of blood stem cells (haematopoietic stem cells or HSCs). While much social science critique has of late been focused on embryonic stem cells, relatively little attention has been given to the historical emergence of stem cell biology, especially the importance of blood innovation stretching back through the middle of the twentieth century and beyond. Present-day stem cell networks inherit much from the historical engagement of medical technology with blood, especially in the contexts of blood processing, bone marrow transplantation and, more recently, gene therapy. In making sense of the shaping of blood stem cells this article draws on perspectives in the ‘sociology of expectations’ in exploring the way current expectations of stem cells are historically constituted. In this way we examine the way biological entities—HSCs in this case—become the focus and bearers of future value in contemporary global stem cell economies.