As the use of stem cells grows, the strict definition of “stem cells” is becoming less clear. Although there are distinct markers, like those defined by glycosylation in pluripotent stem cells and hematopoietic stem cells, many tissue stem cells still lack unique markers and are grouped as heterogeneous cell populations, identified by combinations of multiple markers. Large-scale studies, such as single-cell analysis and the Protein Atlas, are currently underway, and it is hoped that incorporating glycosylation analysis will help provide indicators to demonstrate the consistency and equivalence of each stem cell type in the future.